Pet deposits are getting higher and higher. Around here I know lots of landlord who charge $500-$800 NON-refundable pet deposit AND charge an additional $25-$50 per month on the rent for people with pets.
It's kind of like the rent itself. If you like the apartment enough to pay the amount asked for you go for it...otherwise, you just keep looking.
Most states laws that I've browsed do not have a maximum pet deposit, but to be sure check your state laws
here.
If you have problems finding the info, let us know and we'll try to help further.