I sell Ricardo boxes for $12,500 and also a new Crate LS7 for $12,500.....there are other parts required but the engine HP rating is well over 500 and the trans is good for over 1000hp so your comparison of a 400hp SBF is not really very relevant.
My Ricardo transaxles are refurb or take outs from used Ford GT's...a new one is now $18,500 including the mandated $3200 core charge