With $400 you can have one of several excellent (used) amps.
There's a Canadian company called Traynor that used to make amps which were Fender replicas. They made an all-tube 2x12" 100 watt 'Twin' which sounded great, and you can probably find one out there somewhere for less than $400.
Marshall also used to market a range of amps under the trade name 'Park' which are identical (pretty much) to the same Marshall model - it may still be possible to find one of those for your $400.
Music Man is (was?) a company formed by Leo Fender after he sold out to CBS which make (made?) a full range of amps - you can probably find one of their 2x12" all tube 'Twin' amps for about $400.
For an absolute killer tone (but you will need to mic this up) you can probably find an Ampeg Reverberocket for less than $400. Sweet sweet tone!!!
If you're not in a hurry, pawn shops are an Aladdin's Cave. Lots of crap, and then once in a while an absolute gem for 1/4 of it's value. (Offer them 40% of what the marked price is and pay them the 50% they come back with
Also check out the amps at
www.Carvin.com
My experience with them is they are extremely well-made, and sound good. They are (comparatively) cheap as they sell them from the factory; you may be able to find a used one in your price range.
Happy hunting
foo