Difficult to get accurate pricing and as you say no one pays list price due to discounting but I understand an E190 is around $48 million and. 737 around $90 million. True that the leasing pool is much smaller for regional jets but there are plenty of airlines adding Embraer's product to their fleet.
Ultimately it does not matter what your seat cost is so long as you can charge enough to cover it and if you have a monopoly route there is less pressure to discount. Whether there are enough to people who want to travel KTA SIN or BNE KTA is much more of an issue than the type of aircraft they plan to use I believe.