#1
so based on all the advices i got, i have two choices

buy those schaller locking tuners for Fender strats (70 USD investment)
i hear that those fit right into MIM necks with no additional drilling
i also hear that these things greatly help keeping your guitar in tune compared to the stock MIM tuners

OR

buy callaham trem block (60 USD investment)
some say that it MAY not be worth the whole 60 bucks, but it seems that every agree to the fact that this simple block replacement DOES affect sustain and tone

which should i go with? since i have limited amount of money
based on opinions i get, i might even do both later down the road
#2
Personally I'd go with the trem block, or if you're worried about staying in tune, maybe you need to get a new nut. The stock MIM tuners aren't wonderful, but they're not shite either, and I don't think getting locking tuners will help all that much with staying in tune.
Fender Tele
Breedlove SM20
Cort M800

Peavey Classic 30
Roland Microcube

Digitech RP250
Digitech Bad Monkey
#4
I have an 01' MIM strat that I changed the bridge out on. I found a new Wilkinson unit for $30 and it's made a huge difference.

It came with a large heavy block and a screw in arm which were both leaps and bounds better than the stock trem.

The prices people pay for the Callaham stuff are just....... too much, plain and simple.

I've since replaced 2 other trems for Wilkinsons and can say that they are worth every penny spent.

Look here: http://www.guitarheads.net