We are paying $300 for our girl and that's fine for me.. I probably wouldn't go any higher then $400, but thats because of finances and knowing the upfront costs involved on our side too..
I think it's more then reasonable, seeing as she'll come vac'd, sterlised, wormed, checked, and has been cared for by someone for 6 weeks which will include food etc...She's also been checked for behaviour and what not which all costs a fair amount..
The lady looking after her at the moment, has asked if we can get her a new collar and she can keep the old one, as she personally looks after the bigger dogs and collars are expensive.. I have no problems in doing this either!!
I should also state, that we paid $75 for our cat 6 -7 yrs ago from another adoption agency which included vac'd and sterlisation... I guess cats don'e have to go through as much (behaviour tests etc) so they are cheaper? Not to sure!