I have a Kohler SV610-3212 engine on my Husqvarna YTH21K46. Neglected to put engine oil in it now engine seems locked and won't start. Do I have to replace entire engine or can you tell me all the parts needed to replace and / or rebuild. Also what would be the Ballpark cost?

Buy a new engine and put it in.

If you ran it without oil... you can't simply replace parts to fix it. You would NEED access to a machine shop and know what to ask for to have done BEFORE any parts were ordered. Being you are asking this question, it's a safe assumption you don't. That means a professional would have to be paid to do all the work. Assuming its not damaged beyond reair which it is possible it is easily.

Expect it to be expensive either way.

Some of the crankshafts are on roller bearings and you need a special press to separate and assemble. Look for a running used motor first

Hi,
Another option would be a short block; it includes the internal moving parts and you reuse the rest of the old engine. Here is a link to the Courage service manual:
http://www.asberry.net/files/TP-2548.pdf
Peace,
Clarke