@Wil Bischof
Welcome to the expat.com forum and good luck with your transportation calculations! :-)
Did you consider the aggravation factor and the costs of both storing your vehicle and moving it around Europe? It strikes me as a rather complicated solution. To me, it seems far easier to simply rent a vehicle for the weekend in whichever city you end up in.
And, besides, you're not allowing for the fact that most large (i.e. with airports) European cities have lots of central tourist attractions and efficient public transport. I've rarely felt the need to rent a car, I simply stay in a nice downtown hotel, and then walk or use the metro (or a new electric bike/scooter scheme) instead.
Just the logistics sound painful to me! If this weekend I'm in Paris with my trusty Bulgarian vehicle, what do I do with it before I fly out? I can leave it in Paris, in which case I need to pay for a parking lot... and then next week, for my trip to Barcelona, I have to fly back to Paris instead and then drive it to Barcelona.
You also have to plan ahead, rather than enjoying the spontaneity of responding to wherever your airline sends you this week. If they send you to Dusseldorf instead of Barcelona, then the smart play is to hang out in Dusseldorf, not be worrying about a vehicle you recently left in Paris.
I suppose, if you were to spend 200 euros on a weekend rental, and do this every single weekend, that's 10k euros. Which does sound like a lot of money. But airport parking is expensive too, so leaving it at your last city (when you fly out) will cost maybe 150-200 euros for the week. Then driving it to your next city maybe 50-100 euros (or more) in gas, tolls, food.
Or what about time? Approximately, airlines fly at 500 mph, cars do 50 mph. They send you to Dusseldorf, you're there, ready to rock and roll, in 2 hours. Instead, you fly back to Paris, collect your car, and drive to Dusseldorf. That's a whole day lost out of your weekend.
Separately, BulgarianPlates (and BulgarianCompanies and Immigration2Bulgaria) is a website run by a law firm in Plovdiv. They are a good firm, and there's plenty of helpful information on their websites. I've used them for multiple issues, and I recommend them. If you buy a EU car (e.g. in Germany) there are no import taxes or VAT applied here. There's a few hundred in expenses for the import/registration process, and plus their fee (maybe 1,000 or so in total). Plus company incorporation (few hundred). Plus driving car from Germany (also a few hundred).
They registered my two cars and my motorcycle, no problems at all. I bought them on the Ebay (UK) auction site, and then drove them over.