Yes, you can check out the Zip Code feature on my site ViperAlley.Com
I should be able to have the Admin section back online in the next week; we recently upgraded all our products and the Admin demos take a little time to be implemented. To answer your questions:
. You set the cost of an ad per category - the same price applies to all usergroups. For any category you enter:
Base cost of ad:
Cost of highlighting an ad:
Cost of applying bold to an ad:
Cost of applying italics to an ad:
But you have the option of making each item (bold, italics) available to only specific usergroups.
You can limit ads by usergroup in the sense that some usergroups may not be allowed to post ads in some categories.
I'm not sure what you mean "time based subscriptions".
PayPal is the only supported gateway at this time.
You can subscribe to an ad to be notified when comments are posted, but there is not a mechanism for having notifications based on a user-selected criteria.
You can customize any part of the product - all the source and templates are included and not encrypted.
Omegatron (Chuck) does paid modifications for customers if you would like to get a quote on a job.
I hope I answered all your questions, I'll start working on the Admin Demos shortly.