Panties are not actually all that difficult to make, if you have a bit of experience sewing. A serger is preferable but you can make them with just a regular zigzag sewing machine too. They're not expensive either; there's not much material required. You need about a quarter to a third of a yard of a knit fabric (nearly any kind will do) which will easily make 3 or 4 pairs, plus a couple yards of lingerie elastic per pair. If you make thongs, you can probably do 10.
Step 1: Pattern
Take a pair of panties you own that fits how you like, and make a pattern from them. Lay them out on a piece of paper and draw around the edges, making sure to stretch the elastic just enough that the fabric lies flat. I find this is easiest to do by pinning half of each piece to an ironing board with a piece of paper underneath. See the pictures for more detail.
You'll end up with two or three pieces: front, back, and crotch (often the crotch piece is cut in one with the back or front). Make sure the side and crotch seams are the same length on each piece so they'll match up properly when sewn.
I made two patterns, one with side seams and one without; the side seams one turned out better so all the pix, except for those on this page, are of that one.
Step 2: Cutting
My pattern is cut with the front and back on the fold, but not the crotch piece. If you have half a crotch pattern, just cut that on the fold too, twice. You want one front, one back, and one crotch piece of the main fabric, and one crotch piece of lining. An old t-shirt works great for crotch lining!