Any repellant with high levels of DEET will work. I wouldn't even putz with a product that doesn't have at least 80% Deet. Bug netting works too but is tough to fish while wearing the covers. I don't normally suggest DEET to anyone, but if you are headed where the bugs can be bad it will beat a trip from bug hell. Every store up there will probably have an assortment of products but get the highest level of DEET you can find and yes, it will be spendy.
A couple notes.
DEET can be hard on the skin, so when you're away from where the bugs are, wash your hide well to get it off you, then use a moisturizing hand/body lotion. DEET will wash/sweat off, so take it with you.
I've noticed more black flies in the shade or areas where the wind cannot move the air while at our cabin. If I am mowing in the sun, the bugs aren't so bad. Do a shady area though and the blood will flow unless I am doused with DEET. The DEET will ward off deer flies too.