Died while asleep after power went out

My Imac G4 was put into sleep mode on Sunday evening. Monday morning our power went off and on twice suddenly. Now the Imac will NOT power up. I took it to the Apple store in SLO. They say that repairs would be very very expensive. I have data on my Imac that is very important to me, and I run an application off the Classic environment for my business. A clone of the hard drive was placed on an external drive for me by the Apple store. If I buy a G4 or G5, can I run the classic environment? Can I do this by loading 10.4 instead of the 10.5 on the machines I am looking at? I don't want to buy a new machine only to find out I cannot run my classic program. Help!