We'd all love to find a 30-degree, pound and a half, $80 sleeping bag. They don't exist.

Oh, wait, I spoke too soon. Go to Campmor's website and check out the Kelty Light Year 45-degree Ultralight Down Mummy Sleeping Bag Regular - on sale for $90. (While you're there, check out some synthetic bags; I didn't look, but they might have some good ones in that price range. Of course, they'll weigh two pounds or more.)

It's only a 45 degree bag; you won't find one at that price at 30 degrees. However, if you're getting a 30 degree bag "just in case" it gets that cold, as opposed to planning to go out regularly in 30 degree temperatures, it might be OK.

You can do a couple of things to extend its range:
1) sleep on a slightly thicker pad (or two pads, stacked.)
2) sleep in a tent (adds 5 or 10 degrees)
3) wear your other clothing to bed (Campmor also carries a house brand of inexpensive fleece; get some pants, and sleep in your insulating layer and long underwear.
4) Avoid 30 degree weather until you can afford a sleeping bag liner (however, since this works like a layer of fleece, you might just as well carry the clothing which is more versatile.)

That may just get you enough margin that a 45 degree bag will be fine if you usually hike in 50 degree weather, but it occasionally drops down to 35 or 40. (I use a similar technique to extend a high-end 40 degree bag to 25 or 30 degrees, using a down sweater and pants.)

However, if you're planning trips in extended, continuous cold, you only have two choices: pony up the cost of the 30 degree bag, or change your plans.

Good luck. Let us know what you finally choose.