"为了.....，可......“ This means in order to make something, I even do...... “下血本” literal means pay all my blood in, like “all in”. "下了血本" means "下血本" this things is happened. "为了你今天这事，可下了血本了？" I spend heavily on this matter for you.

first of all, you need to separate 可and 下 here, they don't belong to one single word! It might be more clear if you put like this: 这可是 下了 血本 了。 Here 下 means spend/deposit. 血本 means original capital in business (a less fancy explanation) or (it costed them) an arm and a leg (a fancier way to explain). Hope this helps!

可下了血本的意思是使用了大量的资金。 可下=使用也可以=spend