ERWin is the "800 pound gorilla" of data modeling. It can cheerfully handle models that no other product I know of can even contemplate. It is definitely pricey, but much less than $5000.
The high end editions of
Visio will do what most people need, at roughly one tenth of the price of ERWin. Visio brings about 3% of ERWin's capability for about 10% of its price, but that is still more than most data models need. As side benefits, Visio is included in some versions of
Microsoft Visual Studio, and it brings lots of other useful drawing toys to your desktop!
-PatP