Drop spindles are the oldest AND cheapest form of spinning tools you can get, especially since you can make them easy from stuff at Hobby Lobby or similar stores, in different weights for different thicknesses of yarn. Here's how I made my favorite two:
Super-crazy-light spindle:
This one is good for making very thin yarns, which you can either use by themselves or ply to make thicker yarns. Mine weighs approximately 0.2 oz, which is crazy light for spindles.
You Will Need:
Craft spoons ($2)
Dowel rod (less than $1, I like the 4mm)
Drill (or hole punch, maybe?)
Glue (I used wood glue)
Get a dowel rod. Cut off about 6 to 8 inches, round the ends smooth, and cut a notch at a 45 degree angle up into each end, so it looks like a crochet hook. I like to have the notch wider at the outside than the inside, so that the half-hitch you use to secure the thread is more stable and slides in easily (for an example of what I mean with the notch, check out this page's second picture - mine are probably closest to the #5, though I don't smooth out the front quite as much).
Drill (or punch) a hole into the center of a two craft spoons, big enough that you can fit your dowel through it. Poke your dowel through it.
Arrange the craft spoons in a cross shape about 1.5-2" from either end. Since there are notches on both ends, it is usable as either top or bottom whorl. Glue them into place and let dry. You're finished!
Probably More Regular-Weighted Spindle:
This one is closer in weight to ones I've seen folks selling. You should be able to make yarns from DK to bulky. I use it for making worsted weight.
You Will Need:
Dowel Rod (less than $1)
Toy Wheel ($1?)
Glue
Optional: brass hook (maybe $2?)
For this, you want a slightly thicker dowel. Whatever the hole is for the middle of your toy wheel, get that size. Cut off about 11", and either round and notch the ends like before, or screw the brass hook into one end. Me, I likes the notches, but I also have access to a dremel drill.
Put toy wheel on dowel, about 1.5-2" from either the end with the notch or hook (for a top-whorl spindle) or the end without (for a bottom-whorl spindle). Glue in place. You're finished!
Craftin' - A sewing, knitting and glue kind of place.