I'd recommend you to take a GMAT Prep exam first before you start your preparation. The GMAT Prep is the official "practice exam" so to speak, issued by the GMAC. So it uses the actual testing algorithm and from results so far, it seems to be the most accurate, give or take 30 points.
Assuming you have a 45+ Quant score from what you've told us about yourself, I really feel like there's no need to throw away $600 on a prep course. Especially since you mention that you are disciplined enough to study by your own.
I'd recommend a self-study option. Start with the GMAT Prep. As for Math, even though you're at a good level, I'd still advise you to get some good books to completely prepare yourself and not get complacent on any grounds. The
MGMAT Bundle is a good find, I'd think. It's around $200 and has the
MGMAT Strategy Guides + OG12 +
OG Quant and Verbal Review along with the stimulation booklet and marker, I think.
However, if you score at like a 45+ on Quant already, then I'd recommend just getting the OG12 and purchasing the GMAT Club Math Tests (These are hardcore 700+ level materials and they're excellent source of practice). Jeff Sackmann's Sets are also good, from reviews on the site, though I've not used them personally. If your score is in that range, getting math books might not be that helpful, so you can just use the GMAT Club Math Book for any concepts you need and so on.
As for verbal, I'd recommend the
MGMAT SC Guide,
Powerscore CR Bible (Personally, I really like Powerscore's strategies) and any LSAT Book for RC.
However if you like a comprehensive set of books, you could also get the Veritas Book Set for more practice. They've only recently been released and they seem to have a lot of problems that are new. The guides are also organized very effectively into question types, so you can brush up on your weaknesses easily.
So, in summary (This is beginning to remind me of my speech class more and more ..... )
1. Take GMAT Prep
2. If Q>45, don't buy books. Just stick with tests and sets. Or buy books if you really want them :D
3. Buy recommended books for Verbal.
Check out the self study portion of the forum for more detailed reviews on the books.