I bought my Trek a few months ago for £16.50 with a view to converting it for touring duty.
I did 60 miles and 2,850 ft of climbing yesterday to see how we would get on proper touring, short answer, I need a new saddle.
I have a set of rear panniers for it, but wanted to see how it went with the fronts part loaded, the answer is very well.
The things I've changed from original spec are the bars, BB, cranks, chain, cassette, some cables, headset, tyres and saddle, although I may put the armchair it came with back on, as so far I have has an ar$e comfort failure with a Wrights leather and now a Charge Spoon (yes I know, but I've done hundreds of miles on my mtb's in comfort). I've added the racks and mudguards. It is heavy, but it rides very well and climbs well too thanks to the mtb gearing, total cost something like £150 to £200 if that.