How much is appropriate to spend on a dates dime?

I'm going on a date and he offered to pay. I don't go on a lot of dates. I've paid for dates. Gone dutch on dates etc. How much do you think is appropriate to spend on a dates dime? I have always thought it's inappropriate to run up a tab. Especially on a first date just because you know you're not paying for it. I've had people do that to me. I'm bi so I've dated both guys and girls and it's awkward when they start doing that because you don't want to be rude and tell them to stop running up the tab. When you're on a first date and the other person is paying what do you consider to be appropriate to spend