Dana's right. Start with as cheap of material as you can find. If after you work on it for a while, you still have the bug...move on to something else cheap
The point is...you'll probably ruin a lot of stuff at first (we all do). No need to destroy good rock right off the bat. You'll wish you had it later.
On the other hand, it's somewhat easier to succeed in making a decent point if you have decent material to work with.
Start learning to pressure flake with glass. If you want to practice percussion, go with TV screens or toilet tanks.
If you must use flint, novaculite is a good starting point.