If you are serious about comfort on long rides don't skimp on shorts. As the old saying goes, buy cheap buy twice. I picked up a pair
Altura Pro Gel Bibs Shorts when I first started cycling and I wear them every day, yes initial outlay was a bit begrudged (my other half complained a lot about my spending on cycling) but they are really comfy and regularly ride 60+ in them.
http://www.wiggle.co.uk/altura-progel-bib-shorts-1/
Worn them approx 15 weeks straight and they are still going strong, don't focus on the initial outlay, work out how much you are going to be paying for them per day!
While I never condone buying things on credit, (Always pay in full!) if you think about it this way, if they last you only one season they cost a measly 13p/day. 2 years, 6.5p/day, you get the idea
You don't need to buy full bib-trousers too, I stick a pair of
running tights over these (£7.50) and with base layer they will do all the way through winter too.
There is literally no point spending £15 on shorts if you wear them 3 times, its a false economy.