OK, here's one way to make a a relatively inexpensive vocal booth that controls the ambience in a very live sounding room with wood floors and untreated walls.
I started out with a mic stand and the Real Traps portable vocal booth (http://www.realtraps.com/p_pvb.htm) This product did not do nearly enough to eliminate the room ambience.
So here's the first tip. Get your mic stand off the wood floor and onto a rug.
Now head to your local Target or home store that sells window curtains. Find yourself some thick winter-weight window curtain panels, and cheap, light curtain rods.
I like these Target brand, thermal, 50"x84"window panels that are designed to help keep winter drafts from getting in around whatever windows you used them on. They're quilted and padded. $30 each.
I got 4 of them and the associated curtain rods. Total cost: $138
Next, get your tools, measure, and start hanging your curtain rods in a box pattern from the ceiling. 
This will be considerably easier for those of you without cathedral ceilings. Think carefully about exactly where you want to hang the rods before you start drilling holes. I wanted to make sure that I included one of the ceiling lights inside of my booth so that Amy can read a lyric sheet inside the booth.
So here's the first panel hung (with weird lighting on the photo)
As you can see, we're still going to use the Real Traps booth, but it's going to go inside the new booth we're making. Here's the second panel:
I did a lot of test-fitting the rods to get them as close to each other as I could. Here's the third panel.
I will probably be cutting a small window in this panel so Amy and I can see each other during the session (and provide some air!)
Because my ceiling slants, my side panels won't hang at 90 degrees on their own, and the curtains tend to slide down the rod due to gravity. You could sew or velcro them to get them to hang perpendicularly, but as I intend to assemble/disassemble the booth as needed, I just used some some small hand clamps to clamp the panels to each other and into place. This kind of thing:
And finally, the back panel.
I may have to put a foam panel on the ceiling inside the booth as well, but I'm gonna see how this works first.
So there it is. One way to create a relatively inexpensive booth for recording with a condenser mic in a lively room. The rods just pop in and out of the brackets, making it easy to hang or remove the curtain panels as often as you like.