I wonder what kind of bands LegalAID 2018 will draw?
The method for building robotic arms was full of early errors in robotic arm programs(and likely still is), but the programmers identified those errors and fixed them, over and over again. For that matter, programming in general is error prone. Bugfixing happens.
Businesses which can hire ten men to oversee a buggy program rather than twenty men to do the actual work will do so, and over time, the program will get better and need less overseers. Its an iterative process, and one that doesn't need perfect programs to bootstrap.
Tomatos are being genetically engineered to have a consistent size and shape, partly to enable better automated harvesting.
Assuming the 300k is the total cost of the machine, that's replacing, in a shop open 16 hours a day, 365 days a year, a machine that lives for over six years.
Six years, without maintenance...
Furthermore, a small sandwitch shop (a subway franchise) is worth only 90 to 300 thousand dollars. You're suggesting adding a machine worth the cost of the entire shop, on a very high end shop.
You may be able to build an arm that can make sandwitches, but selling it to firms over cheap minimum wage labor (which is easily replaceable and already has all the software necessary for the process...