May be worth a look at that price.
The 400 world is kind of small, and we have a handful of 400 users, somebody may 'know' the bike.
There's no mention of miles....
For the price, if it runs, it may be worth it. If the gas tank is too far gone to fix, it may be a hassle finding another one...and won't be cheap.
If you like tinkering on stuff, the 400 would fit the bill. I'd hate to see you buy one expecting to get a trouble free daily rider. The parts hunt can be frustrating....and working on them likewise.
For less hassle...the SV would work, as well as a used Bandit 600, which may be a better all around bargain. The B6 probably has a lot less character than the other two bikes, but would be great as a first bike.