I get my positives printed at a local blue print shop in town. I have them print it on a transparent mylar and it's a really really good positive but it's expensive. I just did a 17x24 2 color print and the positives were $32...i think it's kinda bucky anyways.
I've heard people print on shit paper and baby oil it but that sounds like a mess.
What are the other alternatives to transparencies?
If you are not going to buy a printer to make films I would go with the oil and paper method. I was skeptical, but I got some 24x36 prints at Kinkos and used the oil method and it worked like a charm. If you are messy it will be messy.
The kinkos that I use has a machine made by Oce that I think they call a zoomer. It is a black laser printer that they load with a pretty light paper - 20# or so. The baby oil isn't so messy. You don't have to soak the paper. Just squirt it down and rub it in with some paper towel. Blot it with some scrap paper, let dry and you have homemade vellum. 16" x 20" prints are $2.
I did the paper, baby oil route for a while and it was tricky to nail down an exposure at first and I was always afraid when I went to wash it out that I'd kill the detail but with some trial and error I got it. Then I bought an epson 1400 and that has been much more consistent and easier, but it is limiting in the 13x19 size -although I will tile the films if the design will allow for it. I also use rubylith for my background fills and stuff like that which can help me increase the overall size of my image area beyond 13x19 - again if the design allows for it.
With a black light exposure unit my burn times with normal film and 200 mesh screen was :45 seconds and if I remember correctly oil and paper with everything else the same was maybe around 5 min. After a few burn failures I was able to burn a screen with just paper and no oil in around 10-12 min. So if you want to do a step test it is possible to burn a screen without the oil mess you just have to get it dialed in.