The kit you are referring to is an aftermarket item and is not comprised of genuine OEM Kohler parts. There is a large difference in price. Some professional engine rebuilders refuse to gamble on aftermarket parts and insist on using only OEM Kohler parts. That fact will greatly affect the cost of rebuilding. Secondly, aftermarket kits sold on e-Bay do not include items such as valve guides, valve springs or main bearings.
Tell me. Are you able to examine a main bearing and determine how much life is left in it? I think not. Are you able to look at a valve spring and determine whether it is weak from age? Again, I think not. Springs must be measured and tested or valve performance will be affected.
Machine shop charges vary widely across the country. I don't know where the OP resides and neither do you. Therefore, what you paid to have work done is not germane to the issue here. The price I quoted was based upon a complete Kohler K being handed to a shop who would then have to dismantle that engine, degrease it completely, inspect all of the parts and then perform work that you do not even touch on. I don't consider what you did to be a proper rebuild. Did you put your engine onto a dynamometer when it was back together to see whether it made 14 HP or not?
Not likely. So you are just guessing as to how good your efforts were. But thanks for your reply because more than anything, you just illustrated the very point I was trying to make. The word "rebuilt" does not necessarily mean what you think it means.