For Trap ...singles, continental, etc....I prefer an O/U ...and the Browning Citori XT with 32" barrels is tough to beat.
On a budget - there are lots of used XT's out there ....but if Trap Singles is all you want to shoot ( vs doubles, or Continental, or Bunker Trap ..) then a good single barrel like the older BT-100 or the newer BT-99 are good choices as well.
Trap shooters are a really superstitious group ...if they miss 3 targets out of 150 ..on a cloudy day, when the moon is in its 3rd stage..and they saw a robbin flying south...they'll sell that gun in a heartbeat ...and buy at least 3 more ...just because !! So every shotgun club out there ...has a dozen shotguns for sale on the bulletin board....and 25 shooters that have guns they'll sell / but they can't be bothered to put notes on the board.
If you want a good used Citori XT - in 32" ( they made a 30" as well / but most guys find it too light for Trap ) ....just ask around ...and I'll bet you find at least 6 of them in a month...some with Gracoils on them, etc....
Here is a used XT - 32" with a gra coil unit on it ...and a very nice Turkish Walnut upgraded stock ...that I bought used about 8 yrs ago for around
$ 2K ....( gun was made in 2002 ) ...and somebody paid at least $ 5K just a few yrs before they sold it.
One of my buddies did buy a Browning BPS Trap - pump gun ....about 8 months ago ...and he likes it a lot...and I think it was about $ 700. I don't see many Trap ..pump guns around ...
but Jack West stocks...makes a parallel adj comb ...for 870's, 11-87's and 1100's ... and its synthetic...and reasonably priced ..../ you might even give Jack a call ...and see if he has any 870's in stock that are all set up and ready to ship with his stocks on them.