Since you said "affordable" I'll toss in my current dope holder as an option.
Velcro w/peel stick adhesive ... small square stuck to the front of the scope bell in front of the scope ring.
Small square of white plastic, cut to the size of a business card, small square of velcro on the back
Grease pencil
Eye dropper w/ lighter fluid for cleaning off the grease pencil.
Total cost was $3 for the grease pencil, everything else was on hand or free. Works in the rain, you're not going to break it, it's in a perfect spot to see the dope when you look up to adjust turrets, and when you're not using it all you don't even notice the small velcro square on the scope.