Going by your stated use I would say you should be fine with 18,000 pounds as your GVW (truck with a full load of fuel should be between 13,000 and 14,000 pounds from what I understand). As far as CDL's VA exempts trucks used for personal stuff. The normal point for a CDL would be a GVWR of 26,001 pounds or more. Since a deuce and a half has a GVWR less then 26,001 pounds then it is exempt anyhow.
If you do call MD look for either the IFTA office for MD or call the state DOT people and ask them if you would need a trip permit for a personal use vehicle. If they say no then keep a log of who you talked to and when the call took place (it may save your backside if you get stopped by a clueless Commercial LEO later on that wants to cite you for not having permits). If they say you have to have trip permits ask them to cite the statute or regulation that says you must have it. I have had a few states do this to me and when I forced them to go back in to their regs to cite the statute in question they found out I was exempt due to not being in commerce.
Are you sure they're A3's? If so that's pretty cheap. The price sounds more like they are A2's. The trick with A3's is that they have a really nice auto tranny and if it fails can cost an arm and a leg to fix. A lot of people prefer the older A2's due to the cheaper multi-fuel engines and manual transmission.
Are there any scales between his place and the VA border? If not then you should be fine. Plus I also found a link to the DMV website about a trip permit (used dogpile.com)
https://www.dmv.virginia.gov/dmvnet/trip_permit/intro.asp
With a trip permit the commercial LEO's should leave you alone as you are bringing a new truck back to your home turf and have not put the truck in to the system yet.
VA DMV site has a page of fees but they do not list the rates for heavy trucks. So it looks like your best bet would be to call them directly.
Commonwealth of Virginia Department of Motor Vehicles
The catch with the fees when getting weighted tags is they group the weight in ranges (i.e. 12,000 to 13,999, 14,000 to 16,999, for example). So try to find out what the weight ranges are beforehand and go for the max number for that range as it won't cost you any more. When I went to get weighted tags for my semi truck in Florida I was going to get tags for 42,000 pounds. But when I found out the weight range I would have been priced at covered 40,000 to 43,999 pounds I wrote 43,999 pounds on the form as it was still the same price. So if you go for 18,000 pounds (as I mentioned above) see where that fits in to the ranges of weight.
If you have any other questions about weighted tags let me know.
Ruppster