Hi, Larry! I second the welcome. Also, thanks for the tip on the wood stuff.
Jessica, I agree with Villa about the ReStore, you can find a lot of stuff at very low prices. I got those lever type doorknobs for $2. But if you don't have a Habitat For Humanity ReStore near you, there are also places like Surplus Warehouse. They actually have some pretty good prices on things. Also, at some stores, if you buy the previous year's stuff or things that are on clearance you might save some $.
If you want a medicine cabinet and can't find one that you like or one that is cheap enough, you can actually build your own using an inexpensive mirror and a 1"x3" board.
Details here:
http://www.iloverehabs.com/2011/04/11/rehab-cheap-mirror-into-medicine-cabinet/ (although I would probably go with a "piano hinge" aka continuous hinge instead of two separate hinges).
Sutherlands sometimes has good prices and there are certain days where they have special discounts for seniors. So you can take an elderly friend with you.
I would stay away from their combo sinks/counters because almost every single one I saw in the store was broken or chipped (but that could just be the one near me doesn't handle things properly).
If you want very small mirrors for accents, they sell some decent ones at the Dollar Tree (I actually have a couple in my room to reflect some sunlight from the windows to light the room since my bedroom lights don't work).
I will say that on some things it is worth it to pay a little more for quality-- especially on toilets. Read reviews to find out which ones flush well and don't splash. (I personally like the Toto Drake with SanaGloss, but it runs around $400).
Sometimes plumbers/contractors can get you better deals on stuff if you have them order the stuff wholesale (or whatever discount they get).
Are you planning to do any of the labor yourself or are you having a contractor do it?
Planning ahead is key. Figure out your layout of the things that will be behind the wall (water supply, drain/waste/vents, electrical, ductwork etc) and figure out how much stuff you will need to build it. Obviously the professionals will come in handy with that, but it helps to have an idea to estimate the costs. Take into consideration that you may want access panels for plumbing (which you can hide behind mirrors or paintings or something on the opposite side of the wall for interior walls).
If you have a cabinet style vanity, consider getting toekick storage (a drawer in the toekick). You can store bathroom scales and other stuff in them. Sometimes you can get between-the-stud storage as well. It helps to make the most of your space without requiring a huge bathroom. I know this isn't exactly a money saver, but I have at thing about hidden storage or extra storage.
I've seen tall mirrors that secretly open to have storage behind them-- that's pretty cool. You can make your own instead of spending hundreds of $. I've seen inexpensive tall mirrors at Big Lots.
Sorry if this seems random. LOL. I hope some of this is helpful.