The detolf itself costs £40. You then need some strips of wood and some 1cm square mesh to make a lid (you can get them cut to the size you want at the diy store). Maybe £10. If you wanted to stand it on two of these kallax units (it fits with a gap between them so both ends of the detolf are supported), they are £20 each, so another £40.
KALLAX Shelving unit - white - IKEA
But if you have something else to stand it on even better. Or two lack tables would work out cheaper
LACK Coffee table - white - IKEA
Then you need to allow £10 to £20 for a wheel, £7 to £10 for a house, and maybe another £25 for toys and cage contents, plus substrate.
The bits and pieces and extras can all add up, but you can make a lot of toys yourself or use a ceramic mug or toilet roll tube toys. Bendy bridges are a popular choice though.
Cleaning - check out Erin's hamsters videos:
https://www.youtube.com/watch?v=Bo44ombbC6k
https://www.youtube.com/watch?v=5jVnEjrXbww