Slumberjack is a well-known brand for inexpensive sleeping bags. Like most of its genre, you can assume that a +5* bag is more like a 15* or 20* bag. However, that still sounds too warm for where you're at. I'll bet it's really heavy and bulky, too! Have you weighed it?

The Campmor mummy down bag is often recommended for those on a budget. It's a 20* bag but is probably more like a 30* bag. The regular size weighs 2 1/4 lbs. and costs $120. www.campmor.com