Yes, you could achieve water column dosing using dry chemicals.
Some people like to do liquid dosing (or require it for their autodosers, etc); in that case, it is as simple as taking the dry chemicals and dissolving them in the appropriate amount of water.
As for the pricing, for commercial products, you are essentially paying for the cost of shipping (due to the weight of water). You would end up going through commercial products much faster (as they are more dilute). For example, a $4 bucket of dry chemical might last you a year or more (depending on how many aquariums/how large they are, etc)
Okay if a $4 bucket of dry chemical might last me about a year, how much would it probably last in liquid commercial form? - and i'm a noob so I'm very new to all of this chemistry. I don't mind dissolving into water but I'd like to know i'm doing it correctly, part of the appeal to me about getting something like brighty k or pfertz or whatever is that it's "already there and ready" but if I could simply know for example to: put two teaspoons of X and Y into 4 oz of water and I'll get the equivalent of something like either Brighty or pfert'z stuff... cool! I just want as much of the guess work out of the picture as possible but I also need to save money too! and I want a supply that will last me.. so the dry ferts are appealing to me if that kind of friction were minimized. I also find some kind of assurance about name brand commercial stuff because of the testimonials and accountability a business front will/should have as opposed to say someone who doesn't... but my' mind IS open. I'm new to all of this.