What are the chances of getting caught botting high alching?

Your best bet is W44 soul wars, like others said. You'll be averaging about 72.4k/hr not counting randoms. Overall about 70.5k/hr. I recommend botting at the most 18 hours a day. 24/7 is just making it obvious.

If your wondering items, I'd go with nature runes. They high alch for 223gp each, which means if you buy 111gp each there'd be a 1gp profit per alch.

Best of luck