Two bikini hair trimming products geared towards women that can be picked up at the drugstore are Schick Quattro Trim Style (compare prices) and Gillette Venus Bikini Razor (compare prices). Made by the two razor giants, but both reasonably priced.
The Venus Bikini Razor has an advantage by not using batteries as the Trim Style does, but it only has one length option. It works easily and doesn't pull on the hair but cuts it very short, close to stubble length.
The Trim Style can be adjusted to three different lengths, so there are more options. Another nice feature is that their Schick Quattro Razor is on the other side, so there's no need to buy another handle for shaving.