Firstly,assess whether or not your hamster is doing anything to indicate the cage is too small.This would come in the form of stereotypic behavior such as bar chewing(I even see this in tank style cages if a hamster gets a chance),obsessive digging(not normal digging,these are very different behaviors),any sort of attempting to chew their way out or escape,and obsessive pacing.
If your hamster is showing even a few of these behaviors,you really need to consider that either your setup is inappropriate for your hamster or that the cage itself is just too small.
Bigger cages that are storebought get really expensive
You could save up money instead and depending on species make a DIY cage,which would be a lot more cost effective and depending on what route you go the price for the overall floor space can be an absolute steal.There are lots of DIY options,including making your own cage completely or you could expand bins using several bins directly connected(I can explain in another post if you'd like)to make a massive but relatively cheap cage.That is definitely not anywhere near all your options though