Which indian manufacturer sells the cheap and good computers that
could be used to set up a computer education and training center? I am
looking for a good balance between price and performance. The
manufacturer should have good service network and warranty program.

low cost PC's from Xenitis 
xenitisgroup.com

In India Zenith and Acer are the brands where you can get the machines
with reasonable price and performance. some times HCL also offers some
machines with less prices.
Also you can opt for assembled machines, which comes for less price
and take an AMC(annual maintenance contract) with some third party
people which can cover all the service/maintenance work required.