From my experience, I'd ebay for a CB-6000, I got a pretty good deal on mine.
I recently got mine, and its pretty much invisible under just about any clothing if you wear some tighter underwear over it. One thing worth considering though is the weight of a metal device might be irritating for someone new to chastity. The weight of the CB-6000 is noticeable when not wearing underwear, but I really wouldn't want any more weight than this, at least for now.
Also, what size options are available for that device. One thing men newly in chastity often have issues with is fit. The best way to do it is to gradually drop spacer and ring sizes. I seem to be pretty sensitive to spacer size, one size too small results in some impressive chafing, so if I were you, I'd look for something that has some adjustability.
Hope I've helped,
Mr. Horner