Honestly, making horsepower costs money - so does getting it to the ground.
Myself, I haven't spent much time reviewing the Monster Transmission site, so I am unable to comment on their products.
An associate of mine does have a big block Chevy in front of a 700R4 with Sonnex parts - the first time was a stock one, and he made it less than fifteen miles. With his, he as realistic in the horsepower he was twisting through it and ended up spending about $4000 start to finish - transmission with upgraded parts, pan, cooler, lock-up kit.
From what I have seen with my own eyes, the extra money spent is piece of mind - it also means some of the improvements I have planned for my engine will need to wait until I have my 700R4 completed properly (I am too cheap to risk lunching the transmission for no other reason than prevarication.)
I figure by the time I am done, my transmission will cost a little over a third of the cost of my small block.