I hope you can get the wart cream and it helps. I can understand trying that first. ÂŁ200 sounds a lot for a biopsy. When I had surgery done it was the other way round. The surgery was done and lump removed and it was then sent away for culture to see what it was - and that bit was an optional extra fee. And she's not that young at 15 months.
There's one here that's a herbal wart cream for pets. Some people seemed to think it worked and others didn't
Thuja wart cream
Bazuka is the only one I'm aware of and it does contain salicylic acid. I think really it would need a vet prescription as the dose might be too much for a hamster. It's difficult when not many medicines are licensed for hamsters.
Bazuka