About 4 years ago I bit the bullet and bought a brand new Stihl strimmer for £135.. to use around the allotment.
https://www.google.co.uk/?gws_rd=ssl#q=fs+50+c-e+price
It has never let me down and starts on the 2nd pull every time. I have just been offered £100 for it, so a well looked after Stihl holds it's value. Everyone else at the allotment has all the cheaper makes and they spend more time being repaired than they do strimming. It takes a lot of bad language to start most cheap strimmers... and they all end up in the back of the shed as they wont start and it costs at least £60 to have a technician look at it.
Do yourself a favour and get a new Stihl .. remember .. no starting problems and they hold their value. If you look on Ebay you will see how much they sell for 2nd hand.