I think the project is going to depend on if the Pistons can be re-used as the new liners are cheap compared to new pistons. (You will not know until they are out of the Engine.)
Another cost+ would be the Crankshaft if it needs re-grinding.
Last year there was a source of new made in Tiawan pistons for N/A 300D; don't know the cost or if the Seller had oversized or not.
I found this Ebay seller selling a set of 5
Oversized pistons for less than $300. Quality???
http://cgi.ebay.com/ebaymotors/Mercedes-Diesel-Pistons-Rings-8mm-240D-300D-300TD_W0QQcmdZViewItemQQ_trkparmsZ72Q3a1205Q7c66Q3a2Q7c65Q3a12Q7c39Q3a1Q7c240Q3a1318Q7c301Q3a1Q7c293 Q3a1Q7c294Q3a50QQ_trksidZp3286Q2ec0Q2em14QQhashZitem250356580162QQitemZ250356580162QQptZMotorsQ5fCar Q5fTruckQ5fPartsQ5fAccessories