All of the labs I've come across in the UK basically have a 400ft minimum order quantity (or the financial equivalent). In my experience they don't care too much how that is made up: x1 400ft core, x4 100ft spools, or various other combinations.
They might get a bit grumpy if you sent them x40 10ft lengths, but within reason they're happy to work with different lengths of film.
Last time I shot 16mm it was with Fuji's now deceased "complete 16" package, which was a significant saving over standard costs. Your best bet is to drop a line to the labs to find their current pricing for process & Tk. Any info. I have lying around will be a few years out of date now.
In the UK your options are going to be a little limited these days. I believe Deluxe actually send their 16mm to Technicolor for processing now (before then doing the Tk themselves), leaving the other possibility as i-Dailies, which rose pheonix like from the ashes of iLab by the staff after their parent company closed them down. Film & Photo have a website which hasn't been updated in years. I'm sure many people find them fine to work with, but my own experience of trying to contact them I found they never responded to emails, were reluctant to answer the phone, and when I did speak to them they were decidedly less than friendly or helpful (in sharp contrast to all the other labs I've ever contacted) - on that occasion my business went elsewhere! (Film Lab North - RIP). I only mention them for completeness, as I think that about sums up all the labs left in the UK now.
Personally I'd try giving i-Dailies a shout, I always found them most helpful when they existed as iLab. Although they don't do processing, I had an enjoyable experience sitting in on an HD telecine session at Rushes, finding everyone there friendly and helpful despite the fact my project only comprised about 500ft of 16mm film.
Edited by Ian Cooper, 08 March 2013 - 06:13 AM.