If you like cromo steel You should be able to get a Trek 820,830 used-rigid- for well under $150- just buy a $100 used suspension fork-Ebay-and you are set.
Pay maybe $225 and get a Trek 930,950,970,990- most rigid some with suspension fork.
In any case- buy used.A $400 new MTB isn't much of a bike-for $400 used you could get a bike that sold for $1000-$1400 5 years ago
PS 3 months back I sold a Griant NRS- full suspension -for $400- it cost the original owner $1800 in 2002. Great street bike, good MTB