I wouldn't consider DIY as a saving in cost... I've priced out 35mm as well as 16mm reversal and negative, and it just does not stack up financially. Consider this... if you're shooting 16mm in 100' spools, and you have a lomo reel, that's two/three litres of chemicals per load. Each liter of chemicals cost $30, so you're already out $90 or you'd have to buy bulk... but that costs hundreds of dollars for each batch, there's issues of scale in terms of physically storing 50 gallons of each solution and the chemistry goes bad if not used within a few months. Plus the cost of equipment, drying space and environmental effects.
If you get a extra-low volume processing unit, like a morse, you'll use much less developer, but you'll have extended processing times and more chance of uneven development... so there would be a learning curve to perfect your technique. So then it's about what you're willing to sacrifice.... money or time. Even if you bought an automated processing machine, they usually need a certain amount of feet to be processed to function well, otherwise chemistry crystallizes and clogs up rollers, goes bad and ruins your film. The average shooter will never have enough film to keep that machine in tip-top shape day in day out.
In the end, if you want to DIY you have to want to do it for the joy of the process or want a specific effect not obtainable from your typical processing house. Nothing beats 14c - 21c per foot...
-Jesse-
Just re-read your post, and wanted to address specifically your desire to do test rolls DIY, and thought I'd add one more thing... if you're doing DIY you'll have more issues with quality control... if I'm doing test rolls I want to know that all processing variables are minimised.... doing my own development introduced some pretty wild curveballs, UNLESS you have a specific quality control pipeline for your processing and follow it rigorously.
-Jesse-