So in a rare display of initiative, we went to Lowe's tonight and bought the PVC pipe and fittings for the seed starting stand - I had Zack cut the pipes to length and I put it together in about half an hour. I only made it one shelf high, rather than three, for economy of both space and money.
The pipe and fittings together cost less than $20; if I wanted to add another shelf it would be only about $5. The lighting will be a little more expensive. Each fixture was $9 and the bulbs are $7 for a pack of two, so I'm looking at another $32 for that. But this is something I can use every year, so the expense is sort of amortized, if that's how you use that word.
Here are all the bits:
Unfortunately my usual failure to properly estimate size has come into play - this thing is too big to fit into the closet, I think. So I need to figure out another location for it where the cats won't get to it. I'm thinking of just keeping it in the office and closing that door when we aren't in the room. This will probably result in much feline frustration and meowing at the door, but Audrey does that to the closets as it is; what's one more door?
Even with the size issue, I'm pretty happy with this. It was fun and really easy to put together, and cheap. It's given me all sorts of ideas for other PVC furniture, too. Normally I'd rather avoid plastics when possible, but I've got so many other, more major changes to make that a few PVC pipes here and there aren't my biggest contribution to the decline of the environment, really.
Now I just need to research which type of fluorescent bulb to buy, and even more anxiously await the arrival of my seeds from Baker Creek!