Build Advice 3D printing service?

Commercial 3D printing services are not cheap, sadly. When you're printing at home, your costs are only the material (call it 5p per gramme as a base price) and the electricity (50-100W for your average home-user-targeted printer). So, if you're printing a Raspberry Pi case which weighs (throws STL file at estimator) 90g and takes (throws finger in air, makes a guess) five hours to print you're looking at a cost of ((90*5)/100) £4.50 in material and (average (((75*5)/1000)*12.5)/100) 5p-ish in electricity. £4.55, not too shabby. I mean, there's depreciation and maintenance on the printer to throw in there, but let's not overcomplicated things.

For a commercial service, though, you've got a bottleneck: they only have so many printers available. For all the time a printer is printing your file, it's not printing someone else's (yes, I'm aware you could merge a bunch of files together into a single big file up to the total footprint of the print bed, but if there are four five-hour jobs in there it's still going to take close to 20 hours whether you do that or print 'em one at a time). That's the biggest contributor to cost: they have to set the cost to a level where they're controlling demand, so they're not overwhelmed by too many orders for the number of printers they can run.

That, sadly, bumps things up considerably. Pulling a random Pi case from Thingiverse and throwing it at DirtyPCBs' SLA printing service, you're looking at... $89.59 a chuck. Ouch. If you're happy waiting 21 days for it, 3DPrintDirect will make you one for £36.10 plus delivery - less ouch, but still ouch.

Your best bet, if you want these things to come in at less than the cost of a commercial case, would be to ask in the Marketplace for someone with a printer to run 'em off for you or to get in touch with your nearest hackspace or makerspace. The second best would be to buy a £100-200 printer, print what you need, then sell the printer on.