If I had a dollar for every thread I've read in the last 10-years where someone want lots of horsepower, but doesn't want to spend much money I would be a millionaire.
With the cost of parts today if you want a true 400 HP small block from 340" your going to spend some "Budget Breaking" money. No way around it.
That depends on if one has a actual reasonable budget, and how much work you are capable of or plan to do yourself. If you have a good core engine already, 400 hp with a 340 isn't exactly setting the bar too high.