I think just always checking Ebay would be your best thing to do. Clearly if your wanting to get into ULF, its because of the quality of print that can result from that size negative, so the suggestions about making a pinhole camera to put a piece of paper in are just silly! That would be a pinhole camera, not an ultra large format camera guys! Also, many people have made comments about an 8x10 camera, well...8x10 is not "ultra large format", just so everyone knows.
I purchased a Burke & James 11x14 off ebay for about 1,400.00. I also got 8 film holders and a couple lenses, and all together it has cost me about 2,000 for everything. I suggest getting a credit card and just putting everything on the card and paying it off as you can afford. I know alot of people don't have 2,000 bucks to throw down on a expensive camera...but the cost of ULF cameras and gears is NOT GOING DOWN...ITS ONLY GOING UP!
The suggestion about trying to find a camera with rotten bellows is not that good of an idea. Most people bidding on Ebay know how much the camera will be to repair, so they all bid about the same amount less then what they normally would. It would be best to get a camera for 1,500 bucks, rather then a damaged camera for 1,000 and have to invest hundreds of dollars for custom bellows and refinishing, and hours or time invested to fix it. Time is money.
Just get a camera that is in good working condition, and take care of it. It will probably never go down in value, so you could always sell it for more money later. Ebay also offers a "buyers credit" if you dont have a credit card.
I just say to dive in with both feet first, because there is no REALLY cheep way around ULF. Keep you eyes open for deals and take advantage of them.