Soy protein is a very cheap protein to manufacture, in comparison to whey.
As for the quality, there's something intrinsical here: Whey is animal-origin, while soy is notl. We know the old afage about non-animal protein being incomplete... then again, not all animal-based proteins are hight quality (colagen, for example is also animal and cheap).
If you can afford (both in money, taste and variety) to eat more real food and whey to COMPLEMENT your protein intake, you wouldn't be in a bad position.
If you want to mix things up a bit, change to soy for a number of days, the most common mistake we all make is trying to have absolutes and say "I will only use soy or whey or this or that". Variety is key here, both for results and your sanity.