Timing is a big factor around here.  Almost all farmers have their own sprayers these days (mostly SP) and coops custom applicators are cutting back.  This year it was either wind(mostly) or temps(too high or too low) that made timely spraying a real challenge around here and availability of custom sprayers - nil.  Had a weed problem in a few acres on a field 45 miles away.  Wasn't worth dragging our sprayer up there so contacted a custom sprayer to we have used in the past.  Said he would get to it when he could.  Never did get to it and then quit returning my calls.  We ended up spraying ourselves 2-3 weeks too late.  So barring a major breakdown I am done with custom applicators.  Have also had custom applicators spray when it was too hot just to get the job done.  Complete waste of money if you don't do it right.

If you have good reliable applicators in your area then the decision is different.  But in W. Nebraska owning your own rig has almost become a necessity.  SP vs pull-type.  Depends on acres.  Can't go nearly as fast with a pull-type and our fields not that smooth.  That being said, maintenance and repairs on a SP rig is a significant factor if you have to buy an older one (we have a 12 year old Hagie).  We farm 6000 acres - mostly dryland and some pivot.  Would not want to go back to a pull-type.