Regarding the sales tax issue, here is how it works in California: I can only imagine other States are somewhat similar.
Say you live in another state and came to California to specifically purchase a particular car or circumstances dictate that you purchase one while visiting friends or vacationing (??). To avoid being required to pay California tax even though you are a resident of another state you must take physical delivery of the vehicle and the seller must have signed documentation consumating the sale that was executed and notorized outside the State boundries and the vehicle cannot legally re-enter the State without License fees becoming due. California DMV would issue what is called a "One Way Trip Permit" (10 day temporary license tag) that the vehicle could be operated on while in route back home, placed on the car once outside State boundries. Then when you arrive home you go to your local DMV and pay for the necessary licensing & get plates and then (as some States require) go separately to the local tax or revenue office to pay the required Tax. If you bring a newly purchased vehicle into California from out of state The DMV collects the required tax at the time they issue plates & registration. I will not touch on the impact that the Smog issues or the Bureau of Automotive Repair (BAR) play in the process.
Purchasing a California registered car that has been through the SB100 can save an imense amount of stress and work.
Try looking here:
http://www.cobracountry.com/cobrasforsale-cobras.html