Thanks everyone. Well, I found out that J & K cabinets (a large RTA cabinet distributor) had a local dealer not too far from me, (Global Home Products in Beltsville, MD) so I called them and they actually had the size and color vanity I wanted in stock. The price was $199, and assembly was only $10, for an all wood, painted white shaker style vanity. Even the center panel on the doors was solid wood --a true reverse raised panel (almost every RTA cabinet seems to use MDF for the center panel!) The cheapest, similar, special order cabinet from Home Depot or Lowes would have been between $300-400 (American Woodmark or Kraftmaid, etc.) I checked with Barker cabinets and they were quite expensive in comparison.
When I got to the dealer, I was surprised to see what a large showroom they had and how busy they were, even on a weekday afternoon. I believe that all their cabinet lines were RTA, and they had very good prices. The display kitchens and vanities looked very nice. The place seemed to be run mainly by Chinese people, ( a little hard to understand their accents, but very nice and helpful) so I imagine they don't have any problems communicating directly with those factories that make their cabinets over in China if they need to!
Anyway--I'm glad that I had them put the cabinet together, as when they opened the box there was some minor damage to the face frame part. So they used the face frame off the identical vanity that was on their showroom floor and were able to assemble my vanity. It does look gorgeous--esp. the doors.
Even the back is solid plywood with wood bracing. I suppose that makes it more sturdy, but it will be more work for my husband to drill holes for the plumbing.
Hope this helps someone else who might be wondering about RTA cabinets.
Q