Muriatic Acid is very dangerous and it does not matter how much it cost, there is not much use for it in pressure washing unless you have exact, specific uses which 98% of the time you have no need in most pressure washing jobs.
Price on chemicals should not matter, what the chemical is, how dangerous it is and what it does should be what matters to you.
Like Russ Mentioned, unless you want to etch concrete (like melting it) for applying specific coatings in heavy duty settings or industrial applications, I would stay away from that stuff.
You can almost always see in the Home Depot, Lowes, and other hardware stores where someone spilled it on the concrete floor where it ate through some of the concrete. Most customers don't want this happening on their concrete and I am sure that they would get really pissed off and/or take legal action if you tried it for some unknown reason.
This is one of those chemicals that there are not a lot of uses for, is dangerous and can easily cause permanent damage to most surfaces and/or yourself.
Hope this helps.