My view
Both GC and CBJN have a positive expectation for anyone that uses them. If you are on a limited budget, then I would rank positive EV expenditures as follows:
1. The core books that should be in every players library (Professional BJ, BJA). These books will give you the highest return on your investment (even considering the cost of your time to read them).
2. Good software for calculating your betting approach (I would recommend either BJRM or CVCX)
3. GC membership
4. CV Blackjack for practicing. I also really like the Deepnet applications for the iPhone.
5. CBJN
6. Other BJ books beyond the "core" books above.
YMMV, and others will disagree, but if I had it to do over again, that is the order that I would focus on.