Re: Which Marshall?
For Marshalls, I like the Vintage Modern and I like the older JCM2000 DSL 50. Wouldn't necessarily turn down a good JCM 800 or the right 900 either.
If you don't necessarily have to have a Marshall, per se, there are a lot of other good amps that have British tonality that might fit in your budget. I like the Mesa 50-watt Stiletto Ace; it came in a 112, 212 and head version. If you want MORE, there's the Stiletto Deuce and Trident. I see Stiletto Deuce heads and 412s in my area within your budget. And then there's Blackstar, Orange, Hiwatt, etc.
Good luck!
Bill