I guess my first question is this: How the heck did the bag get so wet when you were camping on a snowfield? There’s certainly no reason for that-the Slickrock’s floor is waterproof. I suppose there may have been a condensation issue, as in June the temperature is apt to be moderately high, and warm air from the tent occupants or the ambient atmosphere could have condensed against the tent floor. Still, I’ve camped on snow plenty of times, and so long as the bag is on a sleeping pad, it stays adequately dry. So maybe the first thing to do is use a full-length pad-if not a full Therm-a-Rest, then perhaps your 3/4 model coupled with a lightweight non-inflatable pad. A simple Ensolite pad would be fine, or the Cascade Designs Z-Rest (15 ounces; $36). Adds a little weight, I admit, but doesn’t cost much.
Otherwise, the best solution will be a new a synthetic bag. I wouldn’t bother with a down-filled bag that has a “waterproof” shell-they’re water-resistant, anyway, add $75 to the cost, and cause other condensation problems by trapping moisture inside. One reliable favorite in a synthetic is The North Face’s Cat’s Meow ($169, 20 degrees, two pounds, 12 ounces). L.L. Bean’s Summit 3D 20-Degree Mummy offers similar specs (although it’s a bit heavier) for $139.
A third choice: A bag cover. Outdoor Research makes a very fine sleeping bag cover from Gore Dryloft, the stuff used by many bag makers for their water-resistant shell. It weighs just a pounds, but costs a rather steep $142. I haven’t seen any water-resistant bag covers listed at Canada’s Mountain Equipment Co-op, but you might check the store to see what they have. Makes sense that there would be something more affordable there.