2m worth of item is equal 1 usd in RMAH, 40m would be 20usd, that's the easiest way to sell item - by applying this rate to the item you sell at RMAH, but we usually make it 1m = 1 usd with items that have rare stats, for example a rings/amulets/gloves/boots and such, especially items that when u insert their main stat at the AH, only 2-3 items have equal or more stat than it has, those kind of item sells high on RMAH. The kind of stats you have to look, it varies, everyone has different stat that they want, so almost every item have their own value.
example.
A belt.
150 dex belt = 10k
150 dex 100 vit = 150k
150 dex 100 vit 50 all resist = 2m
150 dex 100 vit 50 all resist 7% life = 5m
150 dex 100 vit 50 all resist 7% life 7 pickup radius = 12m
150 dex 100 vit 50 all resist 7% life 7 pickup radius 20 magic find = 30m
if u don't have this kind of knowledge, the knowledge to know prices just by looking at it for 1 sec, then go learn it first. I know the price just by first look on rings, belt, shoulders, amours, boots and rings. this is my category, pick your own category and own them, 3 category is already good enough, you might wanna learn prices by watching a bid till the end as well.
rares sell in rmah ? mine's not selling , all of my items sold in rmah is legendaries