Pentax AF200T or AF280T would be a good OEM options. Vivitar 285HV is/was a great workhorse for $80 (they've been bought by Cactus so reliability and quality may be an issue - I have no evidence one way or the other). Lumopro, working with mpex.com, who are in David "The Strobist" Hobby's left pocket (whew!) have just come out with the LU120. Even used Nikon SB24s would be just fine.
Since you're doing off-camera flash the brand really doesn't matter. You just need it to be:
a) Adjustable (3 stops minimum)
b) Have a sync port - or if not you'll need a $12 hot shoe adapter with a PC socket.
c) Guide number of 100.
Nice to haves:
d) Zoom - manual or electronic doesn't matter
e) Guide number of 120 or better.
f) TTL so you can use it on-camera and make use of in-camera metering.
You should be able to get a "good enough" flash for no more than $120. Stands and umbrellas can be had for about $30 each. An umbrella swivel for $20. Cactus V2s set for $40.
MPEX has kits pre-configured that are "sanctioned" by The Strobist. You can mix/match/build your own from their inventory as well. But shop around Adorama and B&H as well, because MPEX isn't always less expensive.
Don't worry about backdrops and gels and snoots and gobos and scrims and bookends and ...... you'll learn all about 'em in Lighting101, and most you can make yourself with a cereal box and some gaffer tape.