Blended whiskies are usually a little cheaper and not as good quality as single malts.
ASDA do some good cheap single malts, whereas Glenmorangie do some very nice blended ones. So it's not an exact science. Whisky ages in the cask not the bottle so the older the better.
Are you looking to buy some for a prezzie?
Grain whisky is cheaper to make and used to be the tipple for the drinking population because of the lower cost.
Single grain whiskies are available and some are hideously expensive. I've only even tasted one single grain and never felt the need to try it again. The addition of various malts makes a cheaper and more palatable drink.
There are also blends of malt whiskies (no grain). These are called 'vatted' whiskies.
if you are looking for a lovely single malt that you dont want to be paying too much for then get Glen Grant!! you can only buy it from specialist wine and whisky shops. try looking online! i got mine from my local specialist wine shop for �14.99