When I was still w*rking, we used to use Hudson sprayers exclusively, because they were widely available around here, and you could always find replacement parts for them. They cost about $20-$30 the last I saw. We also used them for applying wood preservative....a lot faster than with a brush!!!
I have a small 1 gallon sprayer with the hose and wand, (similar to the one in T-Al's post above, 'cept much smaller) for spraying insecticide around the house foundation and the garage. I use it a couple times a year. It's some off-brand that I bought for about $10 several years ago.
I also have a couple of off-brand pump-top 1/2 gallon sprayers with the nozzle built right into the top for spraying insecticides (seldom) and fungicides on our roses and a few other plants and bushes. I think they cost about $7 each.
I also have the Weed-Be-Gone and Roundup gallon containers that I bought several years ago, that have the hose and trigger spray nozzle built in, and I buy the concentrate of those products and mix it myself to keep reusing those.