For someone just starting out racing it's quite possible for one bike to serve both purposes, and there's absolutely nothing wrong with commuting on a drop-bar bike. I raced, toured and commuted on a Motobecane Grand Jubilee. The only changes I initially made were tires and freewheel, later had sew-up race wheels. The $500 budget would be a challenge but doable, very doable if a used bike would be acceptable, or could source used race wheels. Just need rims that would work something like a 700x23-25 and 700x28-3.

I think the Nashbar AL-1 is a possiblility - $500, and Nashbar regularly publishes 20% off coupons (one just expired 6/27). If you are not already a customer and would consider that bike I would recommend you register with them, as one often gets a new customer coupon when first registering with a site.