No one is trying to screw you...you don't see the value in the SRT10 so it seems as though you feel like someong is taking advantange of you. There are alot of people on this forum who paid MSRP for their trucks and still love them today. You are attempting to pay thousands below invoice (which is what the dealer pays the factory when the truck is sold) for the baddest truck ever built. Also...the dealer is offering you what they feel is what they are willing to pay for the truck in order to detail it, give it a service inspection, and floor plan the unit (paying interest) untill it sells. There are two types of business entities here in the USA...NOT for profit and FOR profit and the dealer like any other retailer is entitled to make a profit for services provided.
Again...if you feel they are taking advantage of you then have your used truck detailed, take it to a reputable service center and have them check out the unit and provide a written report as to the condition of the vehicle such as a 25 or 30 point inspection, run a Car Fax report which is $20, visit a few banks and ask them for copies of a credit application so when prospective buyers need financing you are prepared, then list it yourself on Auto Trader and sell it yourself. If you sell the vehicle you will then need to make sure you go to the local county tax office with the new buyer to transfer ownership. You will probably have to wait in line for a few hours at the government taxing authority to transfer ownership, pay title fees, and sales tax. Make sure up front you clarify who is going to be responsible for all of the taxes and fees so you yourself don't end up footing the bill which could be $1,000 or so. You want to transfer ownership so if the new buyer has a Hit and Run a week later or illiegaly parks then the license plate tags don't still show you as the owner and you have to hire an attorney to represent you in court to prove you were not downtown that night at the bar because you sold it a week prior. You also need to make sure the new buyer has purchased at least liability insurance in case they are in an accident god forbid you don't get in the middle of that fiasco of who is leaglly responsible.
After it is sold (hopefully for more money than trade in) you can revisit the dealer and attempt to buy the vehicle again. If after all of that you still can't reach a price you are willing to pay for the vehicle then you may have to look at a vehicle that is priced closer to your comfort level of either cash out of pocket or monthly payment. Good Luck!