Do you mean taking in a pack frame with a dry bag attached to it as the bag? What is mid range price to you? 400-600? 200-400?
I don't know if it counts as mid price point, but Kuiu makes pretty light packs and you can get them on sale for 25% off new several times a year at sales. Like a full kit is around 6lbs or so. Usually they have on in May for memorial day. You can also check the classifieds or ebay.
A lot of folks like mystery ranch too, but I'm not sure their price structure, I think they are in the 300-400 range though.
I used an external aluminum style Cabela's pack on a moose hunt when I was younger. It did fine, didn't have a fancy meat shelf or anything and it didn't have a gucci belt, but it worked. You could check garage sales for stuff like that. It would be pretty cheap though for cost saving. My dad still has a pack like that.
I wouldn't do a drybag alone just strapped to a frame pack though. I would bring one in my pack but not as my pack if that's what you mean. It would work though. It just would create a little organization and layout difficulty, but it would work.
You could always barrow a pack too, from a friend if you have one who would loan it to you. Especially if expedition stuff isn't something you do regularly.
I would also look to something from Exo Mountain gear in the classifieds. Lots of used k3 frame and bag combos for sale in the 400-500 range. Really good quality stuff. They are readily available now that Exo has come out with the K4.