What kinds of things are you paying for, though? Consider there's a subtle, unintentional message if you insist on paying for their $20 burger and drink: "This $20 is a big deal to you, but not to me." Unless they are dirt poor, they can probably pay for themselves for most things.
Myself, I have friends with 10x less money (self-employed), and 10x more money (huge stock options and the company popped) -- in both cases, we round-robin the check at dinner. Now mind you, we're not going to French Laundry...