If I was doing that for a heavy truck with rpm's nothing like a high strung engine, then the majority of parts could be much cheaper. You do not need some of the really expensive stuff, but you do need a trusted engine builder. Someone who slaps stuff together is not worth any amount of money, and the parts store sources will have some of that(poor quality control, random lemons).
My 347 was just under $5k back when Woody would build a stock block 302 based engine. The costs have gone way up, the bigger and best heads now run close to $2k alone. You can find decent heads that are under $1500, but I'm not sure of flow numbers, or if they all require roller rockers.
I'd spend good money on the builder and thus machine work, with a stock block, but better heads, pistons, and camshaft. You would benefit greatly with heads that flow 230cfm at least(stock are under 190cfm), but ideally you'd want something that doesn't require roller rockers(likely 95% do). Roller rockers are louder and can be installed poorly(louder and wear faster). The 347 is a great place to begin, but finding a solid block given how rare they are becoming, might be hard. The stock intakes flow 260cfm, the stock heads are under 190cfm and that's the biggest engine bottleneck. The exhaust is a known issue, and the intake elbow is hard to improve.
Decide on fuel, how much will it be driven etc. If it might be driven a tons, and/or you need the cost savings, limit the compression for regular gas(obey what the cam designer tells what the compression can be). If premium is doable, then the compression can go to the 10:1 level or a little more. The right cam can make the engine smooth and reliable with no big issues of tuning, but that's only really possible with a custom cam made for the vehicle combination. Plan it from the start, and the extra cost is minor, say $200 give or take.
The SOHC V6 takes regular fuel with the stock 9.7:1 compression, if a person changed those cams the wrong way, the engine would ping badly and have to be retarded. The cams are a big reason the SOHC runs well with regular fuel, and no big gain from premium.