I'm a great supporter of the cheaper end of the market. My success/ failure rate with them has been no better or worse than with stock from more expensive suppliers like nurseries or specialist growers.
Where they really prove their worth for me is:
1. If money's tight, it doesn't exclude you from growing fruit;
2. If you're starting out you can gain your experience (i.e. make your mistakes) on the cheap ones
3. If it does turn out to be a duff plant (otherwise known as "today I bought a stick"), it's not such a big loss.
Among the bargains doing fine in the garden right now are several blueberries, raspberries, blackberries, tayberries, gooseberries, elderberry, rhubarb, apple, pear, cherry, nectarine, kiwi, orange, kumquat, and a grapevine - all thanks to Woolies, Lidl, Wilkos, Poundland and the 99p shop. The dearest were the fruit trees from Woolies at a massive £7.99. They've all fruited.
Oh, and I just got two more blueberries today from the 99p shop - well, I couldn't just walk past, could I? ;D
Mind you, I gave the redcurrants a miss as they looked a bit mildewy. :-\