<font color="blue">I was thinking of a 3-point spreader and a tank sprayer.</font>
That is exactly the route I went. Spreader for "pelletized" fertilizer and the sprayer for the other lawn treatments. It works great and it will save you money.
It seems all the commercial lawn services here buy their supplies from an outfit near downtown OKC. That outlet also sells to homeowners. I'd never seen 2 1/2 gal. jugs of Round-Up concentrate before. Finding out where the commercial lawn guys go may give you a price comparison to the Ag store.
I recommend fertilizer in bags. If you buy enough for a couple applications, it will save you a trip. The fertilizer will reliably stay in good shape for a few weeks in the bags if the bags are well sealed. Much longer than that and moisture has a way of finding a way in. Maybe not in every bag, but in a few. Take my word for it, moist fertilizer does not spread well at all.
Whenever I'm through spraying, there is usually a little chemical left in the bottom of the tank. I drain it into a 2 gal. pressurized hand sprayer and use it to touch up areas around the lawn.
By the way, got the 55 gal. sprayer from TSC and the spreader from my local JD dealer. Of course, TSC has spreaders, too.
OkieG