Another option is the Ferplast Duna Multy
The only place I know that sells it for a reasonable price is Porton Aquapet. It's 71cm x 46cm and a popular cage for a dwarf hamster and not too tall so no worry about fall risks.
Duna Multy
https://www.portonaquapet.co.uk/shop...a-Multy-M36261
When you say two hamsters, do you mean a pair? Because I think most people would recommend only getting one dwarf hamster rather than a pair. They almost always end up needing separating due to falling out (it can happen suddenly and they can maim or fight to the death). If it was for a pair you would need something a bit bigger than the Duna Multy ideally as well as it needs setting up carefully with two of everything.
Personally though I prefer barred cages, and yes bar spacing for a robo does need to be less than 1cm. Our Robo is in a cage the size of the Hamster Heaven - it's the identical cage really but with narrow bar spacing and without all the colourful plastic things. It's the Savic Mickey 2XL. But - it is expensive new and rare to find second hand.
As someone else mentioned, Pets at home now do an "extra large" wire hamster cage which is about the same size as the duna multy linked above and not too tall.
Pets At Home "Extra Large" cage - maybe not quite large enough.
http://www.petsathome.com/shop/en/pe...me-extra-large
Personally, for our robo I found that kind of size not quite big enough and actually wish he had a 100cm cage.
The Alaska Alpa has for sale would be fine for a Russian dwarf but I wouldn't put a robo in it due to the height and bar spacing, but it would be a good buy for a Russian dwarf - a good size and a cheap option
It would still need setting up carefully to avoid fall risks due to the height - either a full level or a careful set up so they can't land on anything hard.
What our robo has enjoyed most in his cage is :- Having both a wheel and a flying saucer, having a shelf to climb up onto and hide under. And having plenty of floor toys and hidey places and tunnels. And digging tunnels and burrows! So they do need at least 4 to 6" depth of substrate so they can have their normal digging behaviours.
They are very active and will use a lot of floor space, providing it isn't too exposed from above - hence a shelf and lots of hidey places and floor tunnels
I think if cost is a big issue then the cheapest option is either the Duna Multy, the Pets at home cage for a robo, or the Alaska, adapted for a Russian dwarf hamster.
Not sure where you've seen the Hamster Heaven, but the new price is very expensive and Zooplus sell it, and other cages a lot cheaper.
The only suitable robo cage with small bar spacing on Zooplus (under £50) is the Barney cage which has really good floor area and 7mm bar spacing, but like the Alaska, is quite tall for a robo - so you'd really need a full level in that. I initially had the Kerry Terrarium from Zooplus for our Robo - and couldn't get one with it at all - ended up selling it - it just wasn't quite big enough in my opinion. Just about, but combined with top access it just didn't work for me. So a slighly bigger barred cage with narrow bars worked better.
A Barney cage with a full level would be heaven for a robo or dwarf hamster! If you are ok with a bit of diy to make a full level.
Barney cage (needs full level for a robo)
https://www.zooplus.co.uk/shop/small...r_cages/189303
The Alexander cage is even easier, but that does cost a bit more - it already has three good shelves in and it's very easy to make that into a full level by using the ladder as another joining shelf and another bit of wood or even cardboard, to fill all the gaps except a narrow gap at one end for a tunnel or smaller ladder up to the top level. Then you could just hang something over the gap so they can't fall down it if they climb the bars.
Alexander Cage - easy to make a full level with just a piece of wood.
https://www.zooplus.co.uk/shop/small...r_cages/174238
The Alaska, Barney and Alexander on this page, are the most popular, reasonably price hamster cages on here. Delivery is free when you buy a cage.
Although the Alexander costs more it comes with everything except toys and a wheel. It has 3 good houses - the long built in one is very popular with hammies as plenty of space for nesting and hoarding. It also has 7mm bar spacing (even though it says 1cm!). There may be the odd corner gap that is slightly over 7mm - I just use cable ties in that case and pull the bars together a bit - but I actually don't think there are any gaps much bigger than 8mm.
https://www.zooplus.co.uk/shop/small.../hamster_cages
If you like the idea of the Barney cage, but not making a full level (I would hate that degree of finite diy to get it to fit!), then this is basically the identical cage but much lower. It is only available from German Amazon but they do delivery and the delivery cost is reasonable.
Personally I think that is an ideal cage for a Robo
I already have a 100cm cage for our syrian so had to stick with an 80cm one for our robo.
Elmo cage - same size as the Barney cage but lower height - ideal for a robo or dwarf hamster. Has a good shelf, a house and a wheel already so only substrate and toys needed.
https://www.amazon.de/PETGARD-M%C3%A...gateway&sr=8-1
I just went partway through the purchase process on Amazon.de (you sign in with your Uk sign in) to check the delivery cost and it's 14.99 euro - it then translates it into pounds and the total including delivery charge works out at £66.75.
It would be an ideal cage for any dwarf hamster. I think the PEts at home one might be a bit on the small side for fitting enough in as the dimensions are maximum sizes and the base slopes in. The Duna Multy would be a better size if you like the tank style.
Attachment 48148