I edited it for 20 gage wit 28" barrels
Thanks
Hard to beat an English boxlock small bore for light weight and good balance. 28" fixed choked guns may be out there, but most that I have seen are 26". And most have 2 1/2" chambers.
I have a Brit 20 (Alex Martin) that meets the requirements. Originally 2 1/2", but chambers lengthened to 2 3/4" (and reproofed). But you'll also find quite a few with short stocks, because a lot of them were sold as "starter" guns for boys, or for women. If you'd consider a light 12, there are plenty of Brit 12's that will weigh less than a Parker Repro, Win 23, or BSS in 20ga. I've owned 4 that weight less than 6 1/4, 3 of them with 28" barrels.
No shortage of German 20's that will fit your requirements. Sauer, Merkel, Simson are the big names. As with the Spanish guns, you won't find a new one in your price range, but there are plenty on the used market.