Anyone know the dif? Sheridan C9, CB9, w/options

Sheridan CB9 Blue 20 W/Forend Mod $140.00
Sheridan CB9 20 W/Steroid Billet Tune $240.00
Sheridan CB9 20 W/Steroid Tune and Extended Billet $270.00
Sheridan C9 Silver 20 W/Forend Mod $150.00
Sheridan C9 20 W/Steroid Billet Tune $250.00
Sheridan C9 20 W/Steroid Tune and Extended Billet $280.00

Here's a distributor's list

I don't know the difference, but some have the extended billet, steriod tune, etc.

I notice one GB seller has a C9 for $100; it looks rather cheap, in the forearm and stock not matching.

I'm looking at the CB9, the Beeman R9, and one or two RWS models. Thanks for the advice on .20 caliber. That seems like a wise choice. I'll probably be buying used. Thankfully my job takes me all over, and I visit at least one new gunshop a week.