I don't know if you're still looking, but Bulk Powders is the cheapest I've seen. They're very reasonable at base price, but if you lurk, you can often get 10-30% off. (They do student discounts too if you have any in the house you can nick the code off).
I have their Unsweetened Pure Whey Protein Powder, which is totally fine for me. Definitely not delicious, but not rancid either. It just tastes like watery milk. It's 5g carbs per 100g and 1.5g per 30g serving.
If you want something tastier, they do the standard fancy flavours too (and actually do tasting packs, I think), but they all obviously have sweeteners in.
I definitely don't feel guilty about using it while LC. I bought 5kg of the unsweetened stuff for £31.50 (as I got 10% off). That makes it, I think, under 19p per serving, which I'm pretty happy with.
If I compare it to my other LC breakfast of choice (2 eggs), it's the same in calories, but over double the protein, and about 1/3 cheaper if I'm going for free range, which I always do. Well worth the little smidge of carbs, in my book.