So you’ve done the research, located an auction with a seller (who is a dealer) whom you trust based on some telephone conversations (risky, but better than relying on feedback numbers), and now are ready to plunk down a bid and potentially buy yourself a nice shiny new (to you) ride. Be forewarned that the final auction price will definitely not be the total you will have to shell out to get that ride onto the road.
When I purchased my Toyota Celica for $16,000 I still had to pay an additional $1,300 (8.125%) in taxes, shipping, and fees. (and I found an incredible price for shipping too!)
State Sales Tax:
The biggest non-auction-related cost will be sales tax. In Maryland, this is a nice 5% payment that you will be required to make to the state whenever you register the vehicle. If you bought it from an in-state seller who collected it, then you simply present the receipt and Maryland will accept that as payment. For a $15,000 vehicle, 5% is $750 so please make sure you figure that into your costs.
If you’re lucky enough to find a vehicle you like within driving distance, this will only cost you the gasoline and some tolls. If it’s a few states over and you don’t fancy a plane trip and a long drive, shipping it is the only other option. When I had my Celica shipped, I used MoveCars.com  to find the cheapest bonded and insured vehicle transportation company I could.
I personally used Nationwide Auto Transport Inc.  and paid a mere $450 (very cheap, it included a movecars.com discount) for transportation from Florida to Maryland in a covered rig. A covered transport will generally cost you much much more than an uncovered transport and my inexpensive little Celica shared a ride with some Porches and BMW’s. The driver, who took the contract because the Celica was small and fit in a spot on the rig he didn’t think he was going to fill, said typically the transportation fee would be closer to $1000 than $450.
Title, Tags, etc.
These are pretty standard costs and the biggest pain will be in terms of time and not money. If you find a dealer in-state, you might be able to save yourself some time by having them handle that paperwork as if you were buying a used vehicle the traditional non-eBay way.
When I was reading the T&C’s of an auction in the Dissecting An Ebay Car Auction Listing piece , I noted that there were DOC Fees of $279.00 that would be added onto the final sale price of the vehicle. Now, when you’re talking about a $15k vehicle, you would think that $279 isn’t a big deal but you don’t want it to surprise you… esppecially when it’s written as the first item in the terms & conditions! There is no deception here.
Finally, there are fees associated with transferring some of the warranties from the original owner to the new owner. The manufacturer’s warranty (typically now 3 years or 36k miles) will transfer without cost but extended or third party warranties typically carry some sort of paperwork related fee to transfer it into your name. These fees typically run somewhere around $50 or so, you might be able to negotiate the seller into eating these costs.