Can you let him out somewhere safe to run each day? Maybe if you can make one room in the house safe enough, even if you have to stay with him and supervise? If he gets a good run about twice a day, the size of the cage would be less of an issue, or can you attach a run to the cage, and leave the door open, giving him more space that way, as that is much cheaper than buying a new cage.
One of my buns loves the cage she went in when she first arrived here, so she has that with the door removed, with one of the shorter sides against the dining room wall. I then have three run panels, one of which is attached to the dining room wall, and one is clipped to the other end of the cage, so it opens like a gate. This gives her and her bonded bun friend half the dining room, including the cage, for no further cost than the three panels. You may need to provide a simple ramp if bun is still quite young, to help him get safely in and out, though mine all managed this with just a towel over, as you don’t want him catching his leg jumping in and out.
.JPG)
.JPG)