I've had a few old Guild hollowbodies, and they continue to be just about my favorite guitars of all time (I have a 1960 Martin D-18 that will probably stay in 1st place for me forever). As far as pricing goes, there are a couple ways to go, but I generally figure out the average of prices from guitars sold on eBay. I'll also google a few of the big shops around the country to see what they are asking. Then, when I have a specific guitar, I'll run it past the members of this forum - the advice here seems to be fair and thoughtful when it comes to asking about prices. Otherwise, it would be best to get a copy of Hans' book, The Guild Guitar Book, if you can - it is absolutely the best way to really see what's available and what you might be looking at. If you can't get one from Hans, it looks like they are also available online. I also check craigslist in the foolish hope that a $200 Starfire III will show up.
As for the production years, I have only owned ones from 1956, '58, '59, and early '60s, and they all had different headstock logos and pickups. The pickups will make a difference in price, so you need to school yourself a bit on those (and ask advice here). As for price, that will vary depending on the model, pickups, and condition. There are some pristine guitars out there that command a premium, and there are some that have some minor issues that are quite attractive at a decent price. For example, I have a 1956 CE-100 on which I'm replacing the fret markers - the old ones shrunk, broke, or were missing. It also came to me with a non-original pickup. I'm replacing the markers with NOS ones I got from Hans, and I have a Franz pickup from a destroyed T-100 that will go in it. Other than that, it's a guitar that I would consider in "Very Good" condition, and when it's finished, it will be a complete Guild guitar, but it will not be the exact guitar it was when it left the factory. When I sell it (after I get the markers in) I wouldn't even think of asking or expecting an amount that a complete, fully original one might garner. I think you might be able to find some of those around.
Keep asking questions here, and when you find one and can be more specific, let us know. And have fun looking.
Dean