I personally prefer the Sea-to-Sumit Reactor series - they bust your budget of 40ish, but with a coupon or sale you can find it pretty close. They have 3 different models, all different weights and temps -
Something important to keep in mind with liners and their temp range - there is no standard for temp range measurement, this means that company 1 can say their product is got to 40* while company 2 can say their product (made of the same material as company 1) is good for 15* of added benefit. When buying consider your own sleeping habits, do you sleep warm or cold? If warm, you're probably spot on with the ratings listed, maybe even better. However if you sleep cold I would take at least half of what they state and bring extra clothes(or something to ensure you stay warm in cold temps).
Like I said, I prefer the reactor series, and my fav is the extreme - I sleep warm in a house, but cold outside, so it keeps me very happy - plus it doubles as my summer sleeping 'bag' in the dead of summer.
Here are some links to their lineup
+1 on the Sea to Summit. I have the Plus and the Extreme and have used the Extreme down to about 50 with an UQ. I like it enough that I converted both to TQs and they are all I use for summer here in Ga. The Exteme weighs 12.5 oz but with the conversion it now weighs 9.