Honestly, pricing these days is really tricky. Certain ponies go through phases of being super expensive and then drop down again. Others seem to be gradually on the rise and haven't recovered from the spike (for example, Sea Sparkle Baby Sea Ponies have got a lot more expensive than the other sets, relatively speaking, because of a spate of auctions where a few went for silly money).
I'm not confident I'm accurate enough with pony pricing to be able to help you out in a formal way, and I don't really have much pony money to spend at the moment anyway until I get paid for my teaching work, but if there are any informal things I can do to help, then let me know. Unless you have baby sugarcake (the last regular G1 pony I need) and plan to sell her for about half her market value (lol), I am pretty sure I can be 100% objective.
Either way, good luck with your pony sales. I'm sure given what you've said that you'll get a lot of interest.