Assuming you found a way to get ads out there and then got $1 eCPM for them that's still just $50/yr or so. Probably better to use this project to promote one that has a better chance of making money. IMHO.

Charge money. Market it to businesses. You're never going to get money out of something like that from advertising, so you have to go the service route.

If you charged $5/user/month, you might have a nice little supplement to your income. Depends if people find it's worth paying for. If not, you're not going to make any money out of it.

Don't bother writing code, just let them paypal you by hand and enable their account by hand.