Here's a bit of a perhaps arrogant question - do you think there is a relationship between cost and safety? I don't want to buy an all singing and dancing aircraft - three wheels and and a seat would do me - to increase the feeling of being at one with the aircraft. If I could buy one for anything up to 5k, I'd be made up, but just want your opinion on this ...
I don't believe there is any significant link between cost and safety for a flexwing microlight. I think the Flash 2a (which are generally pretty cheap) had a bit of a poor reputation, and a couple of accidents in the late 90s. Pegasus XL, Q, Quasar, Quantums, and the Blades can all be found for <5k, and have good safety records though. You won't find a 4-stroke plane for that money, and the 2-strokes are less reliable, but a flexwing is very easy to put down in a field. No forced landing is completely safe, but I'm only aware of one fatal accident from an engine out in the last 15 years, and although on a 2-stroke it occurred from fuel mismanagement rather than an engine problem.
Single seaters are a bit different as they have (nearly) all been deregulated (SSDR) in the last couple of years. The new SSDR are probably all fine (eg. P&Ms Laser, or Flylight's Dragonfly). There is no official permit system though, and it is up to you to decide whether you are happy it is safe. Second hand older single seaters (eg. the Chaser) may be great, or could be an unmaintained pile of junk that someone has decided they can sell now it doesn't need a permit! Worth taking someone who knows the type along to have a look with you.
You asked about permits and maintenance. The deregulated single seaters do not need a permit at all. Provided you have a valid licence/medical/insurance and you can get it off the ground you can fly it. 2-seaters and single seaters which don't meet the criteria for SSDR need a permit. Once a year the plane + logbook needs inspecting by a BMAA inspector and test flying (cost between you and the inspector - maybe 100GBP), and the paperwork sending off to the BMAA for about another 100GBP to get the permit. You'll also need to be a BMAA member for this (about 60/year, including the monthly magazine). You can normally do all maintenance yourself, with the exception of a factory wing strip every few hundred hours.