There are no reliable price guides for used framing equipment. Age and condition are the first considerations. After that the level of desperation of the buyer and seller come into play. He who least needs to deal wins.
If you're knowledgeable enough to evaluate a machine's condition accurately, and capable of rebuilding it, then you can save BIG on damaged/abused equipment. On the other hand, if you're unfamiliar with the item you want, maybe you should wait until you can afford a new one instead. Or find someone who will help you locate a good buy on a used one.
If you're the buyer, the "right price" is the lowest price the seller will accept. Decide what that item is worth to you and make an offer. Sometimes you get to buy, sometimes not.
If you're the seller, the "right price" is the highest price a potential buyer is willing to pay. Decide what minimum price you will accept, and stick to it...until you get tired of waiting.
Another factor is packing and transportation. I once accepted a FREE drymount press, but had to pay more than $600.00 to get it here from Florida. Still, it was a good buy for me, and the former owner was happy to get it out of the barn. Today it looks and works like new.
Some of the very best deals are at trade shows. Pre-arrange to buy a show demo machine (or several), then drive an appropriate vehicle to the show and bring it home with you -- often cheaper and faster than shipping, and you have a perfect opportunity to enjoy other show benefits, such as education.
Good luck setting up your new shop. Remember: it's usually smarter to borrow wisely and save your capital.