For a long time I've simply been using two of those cheap work-lights you can get at a hardware store, suspended a few feet above an upside-down screen covered with a positive and then a piece of glass. (Lately, frosted on one side.)
There was a time when I'd get positives printed on vellum, but this was sort of hit-or-miss, 'cause sometimes when photocopying on to this material, it'd jam and waste a sheet. In order to make sure of contact with the screen, I'd use a spray adhesive to stick the vellum. However, I started to switch to using bond paper oiled with baby oil at some point, and of course this can't be stuck with glue very well.
I was in a mild mood of despair when I started to notice that I was getting blurring in my exposures for the first time (or at least NOTICING it), and I tried all sorts of things to get this to stop, including looking into building a "bottom-up" exposure unit (as opposed to the "top down" one I describe), and weighting and clamping the glass, but nothing really helped.
On the weekend, I finally got myself together to buy some foam padding. The stuff I got was supposed to be 4" thick, but came out of the roll (I should've gone to an upholstery store, geez!) about 1.5" thick, and so I ended up expanding it by soaking it and drying it out. I tried an exposure last night with oiled bond paper, and it was totally perfect!
I very much like this set-up. It doesn't cost so much and now I have nice exposures in about 12 minutes. TO RECAP, from the top down:
- 2 halide work lights, $15 or less each, suspended a few feet from the screen by means of hooks and planks
- a piece of glass, which I don't remember the cost of (very easy to simply get a quote from a glass shop)
- positives, made from oiled bond paper (there is a thread by seripop about this somewhere, but you pretty much just rub oil into the paper with a cloth, carefully) and placed upside-down
- screen, placed upside-down snug against the foam pad below
- 4" foam pad, cut to the dimensions of the inside of the screen. I bought a piece that cost about $40, which I have cut two sizes from. I probably paid too much for it.