*Loan,banking and credit>>>dental insurance

I don't have dental insurance. How much, on average, does a trip to the dentist cost for filling a cavity?

It cost me 400 bucks. They have to x-ray, clean, fill ect......

Where? To answer in your style, here it's about $250, and you figure out the rest :-)
Usually, if you go to a doc with an MDS, it'll cost around 400 bucks in a metropolitan.
I would estimate somewhere around $300. First visit is an evaluation, which usually consists of an x-ray and an exam by the dentist. They will probably make you go back for second visit to (2nd office charge) do the actual work. You may want to look in your local phone book. Sometimes you can find a coupon for the dentist for a "Free Initial Exam", or 10% off any work. Your Sunday paper might have some too.
Good luck.
it depend where you go? where you live do they have Southern Dental or the Castle Dental there are very affordable
depnds on how deep the cavity is....its from 40$ for a superficial one to 400$ for a deep one...tooo deep means a root canal is necessary
If you can't afford to go to a regular dentist because, depending on the tooth and the work that needs to be done to prep it for the filling, it can be up to a few hundred dollars ... try looking into if there is a dental school in your area.
They are usually much cheaper.
Even though they are still students, they are instructed and supervised by a board certified dentist.

Or you can try your biggest hospital in town, they may have a low cost dental clinic.

Other than that, you can try googling 'affordable dentists, dental clinics, (followed by your town and state)' and see what comes up.