Ok, did some more calculations, also on some drones.
Seems the higher the turnover (more common, eg. drake) the lower the profit.
But IMHO it would still be worth it to set up some mineral buy orders (in the highest ranges, that's how i calculated stuff) and get some building going.
We can see how it goes, what sells and what doesnt, how hard the competition is on the selling plane (i know from experience, there is quite a bit of competition on the mineral buying side, but just overbidding others works, esp if you buy stuff in smaller batches (and not by cents, but just 5% over em or something)).
What I did when I set up my smallish mineral buying orders was buying only station wide (no hauling -> no trouble and no risk) and, like i said, overbidding all the orders in non-player owned stations. Player owned stations are far away and in general not accessible to renters.
With mining ops being at a low, Rub absent, and lot of ppl back in hi-sec, I think this is a good way to make some money. And ofc not as much as when we would mine/refine ourselves, but... get real.........
Which gets me thinking... we may look into ore-orders too. If we got refiners that is.