I took this high speed video of Ernests Gulbis hitting, using a $100 Casio Exilim EX-FC100. http://www.youtube.com/watch?v=zlebgMBe7DQ
For stroke analysis it is hard to beat for the price, you have to have high speed, standard 30fps is useless for stroke analysis.
kinovea is a great open source motion analysis program that rivals dartfish for free. http://www.kinovea.org/en/
I have dartfish but actually prefer kinovea.