The short answer, MTH is a larger locomotive for starters, and is of newer more highly detailed tooling than the smaller antiquated 2-8-0 tooling from Lionel.
I suppose you could throw in a possible limited production number as well.
Having said that. The last run of 4-6-2's from Lionel. Which were rather inaccurate for many of the roadnames, due to the overly long firebox, had an MSRP of $1399.