is it profitable to mine bismuth?
As the price of all crypto sphere is dropping, I don't think is worth mining anything right now unless you have free electricity of very very cheap one. Bismuth makes no exception unfortunately, also the difficulty is a bit high and if you don't own some rigs is worthless to mine with just 1 or 2 GPUs.
If you have 1 - 2 gpu's, then depending on how good they are, you 'might' make 1 or 2 bismuth per day at current difficulty. So based on today's price of bismuth maybe about $1 USD.
Bismuth is actually on whattomine in the 'coins' section so you can check it out there if you want something more specific.