Here's a photo of the Concept Excelsior that I bought on eBay for £15, on its first day as a London commuter.
I fitted mudguards which were lying around unused at home (you can see that they were for 700c wheels, not 26", but they will work fine). Other than the longer seatpost and cheepo saddle, no new parts have been fitted. Since the front shifter was knackered, I removed the gear cable and adjusted the mech to middle ring (38T). After lubrication and cable tension adjustment, the 5 rear gears work reliably now. Basically, very little cost and work to get this roadworthy and working at an acceptable standard. The chain had surface rust, but was not stretched - in fact, it seemed hardly used. So, I wire brushed it and thoroughly oiled it. Gearing is perfectly sufficient for London. First impressions are that it rides well, but is heavy. After winter, I'll fit lighter, narrower, touring type tyres, and that will help a fair amount.