Equity positions are very negotiable. Ask for more equity, a lot more, like 1 or 2 percent.
To be honest, I am half-scared of taking equity instead of cash pay. The reason is, I don't understand it as well as I should. It always scares me to think that through some VC-magic, whatever equity I have could end up nearly worthless (possibly an irrational fear since I don't understand the whole mechanism).
Here's the math I do:
share of company * realistic potential valuation * chance of hitting it * expected dilution.
chance of hitting it ~= 3% expected dilution = 50%
So using your example:
0.0005 * 1B * 0.03 * 0.5 = $7500