House Rules:
For training skills, tool proficiencies, languages, or weapon proficiencies you will be using 25 downtime units minus the lower of your intelligence modifier or the trainer's to calculate how much downtime is spent. For gold cost you will be using x 50gp per downtime unit. If one player character wishes to train one or more other players, they may set their own price, but have to spend downtime equal to amount spent by the student with the lowest INT score. One player character may train up to four students at a time.
So assuming a base cost of 25 DTUs -> 1250 gold cost to run the class (same as Hexia's Scroll). I am assuming that this gold is spent on training materials etc. and disappears into the ether.
Malkus's courses run at a discount, presumably to attract multiple students for the one training session which will bring in more gold for the same 25 DTU base cost to train them.
If you're willing to do a Stealth training class Vic and Tears will both do it and chip in 780 gp each, but it will cost you 26 DTUs to run the training due to Victor's low INT. I think that puts you at a 260 gp profit for 26 DTUs (you also gain 1xp per DTU you spend).
If you get up to two more students then whatever they chip in is pure profit.
Likewise Tiria would take you up on the Investigation class as well but if it's just her the 780gp would be a running at a loss.