Any particular reason you haven't spent the last 4 months that we assumed the books were going to be $50 actually saving up to pay the extra $10 for the Player's Handbook? If you could afford the $40 but not the $50... you'd think you'd be using this time dropping your pocket change into a jar just in case.
Luckily for you... since the DMG doesn't release until November, you can spend the next 6 months gathering together the extra $30 you'd need and buy all 3 books together at $150, rather than your planned hope of buying them all at an affordable $120.