This is what I think:
Helmet: $150-300 (can get some decent Scorpion/HJC, Shark or Icon helmets in this range). Just make sure it fits well.
Jacket: $150-300 (probably looking at textile mesh here, leathers are more expensive but I think they look much nicer and protect better)
Boots: $120-250 (you don't need a full race boot, but something that covers your ankle is great. There's a couple brands, Shift for example which has some 'street wear' looking stuff. I definitely would count foot protection as one of the important things to have)
Gloves: $50-120 (I would recommend not to get 'shorty' gloves, get something that at least covers your wrist though and has armored points. Gloves aren't too bad so you could get your 'dream' glove for $300+ if you really wanted)
Additional gear:
-Knee guards or pants - $50 (for guard) - $250
-Back Protector ($100-300) - you probably won't need this if your jacket has something built-in
Once you've had your first spill, you will understand why people wear gear, and what gear is important - I had a small spill and was wearing zero gear - converse, dress pants, dress shirt, no gloves. Could have ended badly but didn't. Learned the importance of gear from that. Especially the boots. Grommets from the converse shoe (which got ripped up) tore into my foot when I slid. It was slow speed, short slide, and on a 125. I can only imagine if I was on my 600 at street speeds.