Usually, anything "Colonial" goes for Q200, or less, often Q150, which is about $18, for an 8 Reale. Anything smaller is of course less. The guys who sell the pieces are kinda like the guys who stand around subway exits, and have 12 watches on each arm, and wanna sell you one. Obviously, their business model is far from appealing to me.
Guatemala is also not a terribly coin friendly country, as the indigenous love bright shiney pieces of metal, and will take a wire brush to anything, resulting in some tragic messes, and they are bewildered you'd pay them 5 times more if they'd just leave the coin the way it was.
I get very, very lucky with the finca/hacienda tokens, because most people hate them, because they were issued by wealthy landowners, so if they haven't gone into the trash, people will almost throw them at you, to just take them. I have several examples that are apparently 'unknown'. At some point, I'll end up writing a book on the Finca Tokens of Guatemala. It's a pretty obscure subject, and I'm one of 3 people I can find in Guatemala who even collect them, and my collection is at least 100 times larger than either of the other two. The tokens do deserve recognition, as they represent a large amount of the history of our country.