In my humble opinion, the Oceanic line gives you a terrific bang for your buck. There are cheaper regs out there, but Oceanic is known for outstanding performance at a reasonable price.
If you're *really* on a tight budget, the Alpha 7 is a good entry-level regulator. There are no adjustments on it and it's not going to breathe as well as a mid-priced regulator, but it's still a very good and reliable regulator. Somewhere on the Internet is a recent comparo of "budget" regulators, and I recall the Alpha 7 was the best choice. These can be had for about $300 at the LDS or $150 on line (Leisure Pro).
If you can afford to part with a few more bucks, then the Gamma 2 is a good mid-level regulator. These are about $375 at the LDS or $200 on line.
I use the Oceanic Delta 3, the next step up from the Gamma 2. This is Oceanic's mid-high end regulator, but it is still very competitively priced ($459 from LDS -- $250 on line).
If cash is king, then I think you might consider picking up some used gear. If you live in a large city, check your Sunday classified ads. Many times a person will take the dive classes, buy a bunch of gear, and then decide they are not right for the sport. These people sell their entire set of gear at 50 cents on the dollar. So look for these ads.
Your other choice is to look on eBay. But I haven't bought gear on eBay, so I don't know how trustworthy these sellers are. My hunch is that if you purchase from a trusted seller, you should be OK.
Good luck. Diving isn't cheap, but it sure is worth the investment!
Thx...Doug