Well, you need a complete gasket kit, rod kit, set of main bearings, and you might as well put in a fresh top end as well. So price those parts out and that is going to be the minimum parts cost.
Once you get the crank out, you will want to send it to a machine shop for the rebuild, unless you have the tools and experience to disassemble, reassemble and balance the crank. This is a job you normally pay someone else to do because of the precision required, and expensive tools required to do it right.
Then there is any tools you may have to pick up, such as flywheel pullers and case splitters, if you don't already have those, or access to them.
There is also the incidentals, like if your cylinder is worn and needs replating/replacement, or if any of the clutch, transmission, waterpump and other parts look to be in need of replacement.
Best case scenario, probably $300-500 in parts and the crank rebuild. Possibly more if there are other problems. Assuming the bike is in decent shape, it is most likely worth fixing it and knowing what you have got, versus selling it off and buying an unknown bike that could be someone elses headache. It can be a tough choice to fix your old bike, or put the money towards something else and part out the old one for cash.