Leaving Thailand after months-long overstay (can't pay fine)

This question has been asked many times, so I guess you've already found some nice resources (one, two) on this topic.

1. You will pay the 20,000 THB fine. Possibly, more. Possibly, after imprisonment.
2. You will receive the "overstay" stamp in your passport.
3. Possibly, you'll get banned from entering the Kingdom, temporarily or permanently; The biggest issue is that you may not be informed about this right in place and get an unpleasant surprise on your next visit.
4. Your goal is to try to avoid imprisonment.

If failed to pay the overstay fine, you'll most certainly get detained and imprisoned.

So, your actions are:

1. Call your Embassy and ask for instructions as they know the thing better than strangers at StackExchange;
2. Ask for a money transfer from your family or friends;
3. Avoid exposing yourself to random police checks, even on your way to the airport. Don't drive the car/bike, don't visit places where random checks can occur (beer bars, disco, etc);
4. Get safely to the airport; you will need several hours to get through all the process, so come early;
5. Walk up to the Immigration counter, hand your return ticket, pay the fine.
6. Expect for a shame of being handcuffs-escorted to the plane.
7. Never ever overstay anymore.

P.S. Jail in Thailand usually means a small crowded room with no furniture or even fan, lots of mosquitoes, sleeping on a concrete floor, and foreigners even need to pay for their meals.
Don't expose yourself for that.

If you voluntarily exit, you will be fined 500 baht per day of overstay (maximum amount of 20,000 baht), you will not go to jail.

If you are caught by police overstaying, you will face criminal charges and higher fines. Jail time tends to alloted primarily for really long overstays (as in years), not for minor overstays.

If your overstay is less than 90 days, your passport will be marked as an overstay and any future visits will be subjected to proving your tourist intentions (departing tickets, funding, hotel bookings).

If your overstay is more than 90 days you will be banned from the country for 1 year in situation one (voluntary) or 5 years in situation two (arrested). Overstaying by one year would be 3 and 10 year bans respectively.

http://overstay.immigration.go.th/advice.html

If you can't pay the fine, you will be at the mercy of the immigration officer handling your case. He could simply clean out your wallet and send you packing home, he could press legal charges against you, he could choose to deport you which could have ramifications on future visas or visits anywhere, etc. You really need to secure funds before going to the airport, contact friends family back home, ask your buddies in Thailand, contact your embassy about loans, etc.

Here's what actually happened to the OP (as indicated in a comment):

So I got to the airport and paid the fine and signed some papers and that was it... booted for a year, but that was it... last minute I got a loan for the fine... I'm sure it would've been different had I not had the fine money... thanks for all the info people.

Someone suggested to the OP that this information is so valuable that it shouldn't be a mere comment, but edited into OP itself. I think OP should actually make this an answer himself, but until he does, I'm putting it here as a Community Wiki answer.

Let the US consulate know, when you plan to fly back.

Also ask them for advice. I am pretty sure this happens to other people.

This is the official Thai gov advice: http://overstay.immigration.go.th/advice.html

Do everything possible to gather the money. 20,000 bht is $600. Whatever you can sell to get these $600 will be worthwhile.

Report the situation to the nearest immigration office by yourself and come clean. If they catch you, things will be different. Do this with enough time before the flight, not just 2-3 hours before the flight. Otherwise, you could miss your flight.

This is the official Thai gov advice: http://overstay.immigration.go.th/advice.html They draw a line between surrendering and being caught.

Do not approach immigration before you gathered the money.