I think you'll find that most places wont insure a hamster because insurers dont see it as worth it.

Vets fees differ. You'll be paying for a consultation fee as well as any treatment. For instance, when our hamster needed an abcess draining and a weeks worth of antibiotics, it cost us roughly £10 which included a check up a week later.
Another hamster who needed a giant abcess removed from it's face needed to be anethatised first, so that plus antibiotics and a post op check cost us £20-30.
The most expensive ive had for a small animal is for one of our chinchillas to need immediate surgery for a ruptured bowel, that cost £350 which didnt include a post op check or any antibiotics. We payed extra for them.

And its worth mentioning, that if your given an antibiotic called Baytril, you need to give pro biotics with it because Baytril uses up all the good bacteria in a animal. I personally done use Baytril were possible, i request another antibiotic.