I've been wondering about this myself. I think if I'm going to use these tools eventually I may as well get them all at once. Do you think buying separate represents good value compared to a set?
There are 2 schools of thought on this.... one school will always suggest that you buy Park Tools (in the same way as motor mechanics often recommend Snap On Tools) They are very good tools and they do Professional down to higher mid range priced tools.
My view is, if money were no object go with the above.....
....but for the rest of us compromise is the name of the game.
As I stated in my posting above, when I reignited my interest in cycles a few years ago, I bought a complete set - which are still giving very good service. I have expanded the kit and bought specialist tools since - but the basic core was already there.
http://www.ebay.co.uk/itm/Bike-Hand..._Cycling_Tools_RepairKits&hash=item416cad2311
Something like the kit in the link above would be a good place to start at just over £30 ..
No doubt someone from the Park Tools School of thought will advise differently - and I acknowledge that these tools are not the best quality... but they ARE a good starting point and will equip you to start doing most maintenance tasks and they will give value for money for the average cyclist. If you're not convinced - just look at the prices of the items in the kit sold as individual items and you will soon see that £30 won't buy you much.