Chris
I think Engine pricing should be an automatic increase of 'x' amount above the 500k base for each level attained. It seems a bit strange to be offering up LVL 30 engines for 500k when people are trying to sell lower level engines for 500k.. may as well make them all 500k and be done with it.
And what purpose would that serve exactly? Why should someone be stopped from selling a Level 21 engine priced at 1mil. a race, a Level 30 engine priced at 500k a race or anything between the two extremes?
It should be the engine makers discretion, as it is. For example a maker may choose to price their Level 30 engine at 500k and attract more customers, but the caveat maybe that the engine strength / weakness per track is set per the maker's wishes.
On the other hand someone may opt to price their Level 28 at 1 million potentially attracting less customers, but offer their customers the desired strength / weakness on a per request basis via in game messaging or external communication methods.