I've used my serger only a couple of times for quilting. Serged seams are not as accurate as sewn seams (at least for me), plus I don't like the extra thread bulk that sergers put into seams. I even prefer my sewing machine for binding.
Sergers are great for making clothing out of knit fabrics because they control stretch by means of the differential feed. They are also great for straight seams when you need to make tablecloths, finish napkin edges, or sew draperies.
In my opinion, a good quality sewing machine is much more helpful for making quilts than a serger could ever be. If you are on a budget, a serger should probably not be near the top of your list of things to buy -- especially if you're not sure exactly why you want one.