Dave, A few years ago most of those V4s could be rebuilt for under $1500 but with parts cost and labor most will cost more than that now the parts aren't cheap unless you shop around a lot. If he looks around can find a rebuilt ready to go for that price or a tad more or way less maybe off ebay, craigslist or auctions but the key thing is to be sure the crankshaft drive end is the same. I got a rebuilt military surplus MVG4D V4 still on the rebuilders crate off a county auction for $40 and they had bought it military surplus. It has the clutch and short stub shaft crank so won't fit skid steers or welders. Most of the V4 Wisconsins in welders, generators and skid loaders have a special tapered end on crankshaft. The Wisconsin engine spec number tells you what crank is in it and what the end looks like or measures. The Wisconsin factory can tell you the exact crank measurements from that spec number. A "M" in front of the V4 designation like MVF4D means military and many of those engines won't interchange for other things because the crankshaft is different and standard rebuild kits won't fit them they had different rods, rod & main bearings, crankshafts, and pistons & rings. The "D" on end means they had stellite hardened valves & seats. I see rebuilt gas engines now on Diesel Engine Trader too like VH4D for $2700.
http://www.dieselenginetrader.com/engines.cfm?ID=80