I would agree that if you are having to pay someone to do all the work, it is likely not worth it. However, it can be very beneficial and satisfying if you have the capabilities and tools(nothing fancy) to do the work yourself.
I bought a JD D105 with a blown 17.5 B&S in otherwise mint...
Forgot to mention, if it is a rod replacement, when you have the piston out, pull the rings and check ring gaps. Since you have it apart, ring replacement is a no brainer if needed!
Have you considered repairing the existing engine? Do you know why it seized in the 1st place? Low oil perhaps? If it's just a matter of the rod seized to the crank, and the piston/rings/cylinder are OK, the repair is pretty basic. Get the rod cap off and double check if piston is free. The...
No hate intended but I have to respectfully disagree with the assertion that the blade should be like a knife. It's well documented on the inter-webs as to the reasons why too sharp is not preferred so I won't repeat them here. A quick search will answer why. Suffice it to say, 'butter knife'...