I've had much the same experience you've had
Ebay is great to catch angry wives selling their hubby's army lol. I've gotten great deals and a lot of the armies I've seen come with a $50 or $100 case too. Great way to get a diverse range of pieces, if you don't mind repainting. But lets face it, for $150 I bought a small GW army case and easily $450+ retail in pieces. It needed repair and stripped/repainted, but even that was fun.
The only thing I didn't see, that I have to add is the almighty Green Stuff.
I'm very inexperienced at conversions and modeling but I'll tell you it is awesome. Maybe read a tutorial, get a couple tools to carve with, a little bowl of water, an open bits box, and you're good to go.
I took the AoBR box and learned to love the green stuff. I spit the cost with a buddy, took the marines and let him have the rest. Another friend gave me $10 for the dread (i'm not a fan of the chaos dreads, but hell some are) and I converted the SM to Plagues and the with the terms I'm working toward 9 oblitz for a fraction of the price, and I have to say that I like mine better than the GW release. I've seen a hell of a lot of conversions that are nicer than mine, however for $75 for GS and models I ended up with 20 plagues and 9 obliterators. Not only that, but now I'm excited about what else I can build for next to nothing.
The kicker is, my models are at minimum table worthy. I suck at modelling and I'm not that strong of a painter either but with a little bit of trial and error I have some pieces that I am very proud to say that I did. Does your GW Obliterator model have pretty tzeentch pink nipples and a bloody blade for a cock? I think not.
I believe you can get the same type of clay at your local craft store for half the price but I don't personally have any experience with it.
"Bah, Buzz, if it means less paperwork I'll take Chaos"
- Warp Darkmatter of Star Command