Actually some of those are so cheap, you can start off with a few, or add strobes as you go along. I started with 1 small flash: The Nikon SB 28, added the Nikon SB 800 when I got my D70, and when I needed more light, I added the Nikon SB 26. The SB 26 sells for about 100 USD on eBay and other small flashes like the famous Vivitar 285HV sells for about 50 on eBay and about 80 for a new flash.
If you indeed choose this path (which from now on will be called the strobist path) there are several very useful resources on (and off) the web for you to learn how to perfect your small strobe lighting technique.
I have deep appreciation for all photographers listed below, they all helped me learn and grow to the photographer I am today.
This is why I am shamelessly promoting sharing their recent and not so recent projects.