I think you need to consider how much work is involved.
You need at least fundamental plumbing and carpentry skills, because it's not going to be cheap to hire it out. To raise the cabinet you have to remove the faucet, then the cabinet, and build a new base and attach it to the cabinet. Then, if the existing cabinet is not open in the back, cut new holes to accept the plumbing because they are probably not going to line up, replace the renovated cabinet and reconnect the plumbing. That's without having even considered whether or not you want to paint or refinish the cabinet. It may also affect any current backsplash mirror placement. I'm with Hub on this one.

How big is the vanity? The larger it is, the more you'll save by raising it instead of replacing it.

You'll save if you can DIY it, because the materials for raising it are pretty cheap, and building and trimming out a new base is pretty simple.

The plumbing costs involved in both are the same, as any new vanity will need holes cut and plumbing redone for the higher sink.

Thanks, house elf and weedyacres. I hope you're right, weedy. It's not a DIY. One contractor said it might be not much more to have his cabinet guy build new cabs. Another here today said basically the same as weedy. Will wait and see how much the new cabs are and their quality. It's a master bath with three connected vanities. Thanks to you both for your input. :>)

Nice job! I like the new finish a lot, and the counter looks great with it.

Nice job! I want to increase our height also but likely to get new cabs as ours are not fixable - laminate.... gag.... and the typical builder's model!!