Hi campbellsa.
Welcome back to our Mattress Forum! 
This Phoenix post is from 2014, so it may not be especially accurate at the moment, but it does list the budget recommendations that he was familiar with at the time he wrote the post, particularly for a guest room.
You mentioned that you are (wisely) considering medium firmness as it will be the best fit for a wide range of sleepers - I agree that this is a smart choice for mattress firmness in a guest bed!
Sleep On Latex has the Pure Green all-latex queen at $1000 even.
Luma’s Natural Latex Hybrid is currently on sale for $1195.
Sleep EZ’s flippable latex hybrid is also on sale for $1099.
As always, feel free to browse the offerings of the Trusted Members I didn’t include here, as it’s likely I’ve forgotten some great options.
I hope this helps!
NikkiTMU