Is there a way to get foil prices to show while trading. I have a Thundermaw Hellkite FOIL I'm trying to trade and the price is significantly different than the non foil.

At this time, there is no separate pricing for foils (or promos, for that matter) in the system. I know Sebi has heard many voices ask about adding that feature, but I believe the challenge is finding a resource that will play nice with third-party sites.

For now, I typically go to another site to find the pricing I want for a foil, and either list it in the trade chat, or have the other party suggest a value (depending on the card).

Yeah, the TCG API doesn't allow it.

Which is dumb because their collection tracker keeps track of foils you buy from their site, so they do have the data but just aren't willing to share it.