No way it's cheaper apples to apples to hire out a conversion. More than likely not even cheaper to do it yourself.
And at $16k budget, no sense spending a bunch of $ to convert a clapped out old van. Depending what you want to do, you could eat up half that budget in materials and appliances/furnishings.
Find one built out. Better bang for the buck.
And if you're just talking a conversion van and not really a class b, then it may be tough to find one less than 20years old. They went out with Cyndi Lauper, Hair bands and parachute pants!