I am an avid market trader, and have played since game launch.
To provide you some suggestions and thought on this matter, and that is 30k per roast is cheap compared to the time leveling your alch to lv225 rank 2.
A typical Lv225 player will have a net worth of (all assets, including equipment) at least 8mil, and that is a conservative figure. Assuming that the typical player will play the game for on average gamelife of 2months or 60 days, and that you used at least 30days of that time leveling your alchemist to 225. Then, you would need to spread the alchemist cost to 30days to cover the time lost in leveling your main.
Also, my assumption is that an alchemist is not your main.
In number crunching it would come out to be 8mil / 30 days will equate to a required min profit of 270k silver per day.
Back tracking through your standards of 10 roast per day, calcite cost, and 50% tax. The cost per roast will come out to be as 48k minimum cost per roast to even break even.
Now, assuming you do not play everyday as most of us are working adults, or made your alchemist the main (you would be losing out on game content). Having a shop with less than 48k roast cost everyday is a waste of time. As such you would need to supplement earning potential with potions(but there dirt cheap, so thats not plausible xD).
For those out here saying that you get free profit from AFK, idiots! crunch the figures first then tell that to me again. Re-doing calculations with AFK in mind would still spread out the 8mil initial cost to not 30 days but rather at most 45days. Re-doing the calculation again and you would have a min roast cost of 30k. Coincidentally enough, the same min costs you have suggested. However at this cost leveling an alchemist would gain no benefit aside from convenience. A convenience that is not needed when you have several alchemist friends.
And having a shop less than 30k is ludicrous, as profit decreases exponentially due to how profit calculation works.
'- Derkein Dragonfang [Klapedia]
PS: Feel free to pm me if you need potions xD. I need every silver of it due to wasting time on alchemist Y.Y