Craigslist has several rooftop carriers in your area for around a hundred bucks.
Roof top carrier
Roof top cargo carrier
KarRite cargo luggage holder
If you are willing to go a little higher they have:
Yakima Car Top Carrier
Thule Excursion Roof Box & Load Bars
I don't know if anybody else out there does this, but . . .
If I'm only going to use something occasionally, I search for the highest quality item I can find on CL, find an ad that has been on there a while, and talk the people down to the lowest price possible. After I'm done using it (usually a large power tool for a side job) I re-sell it on CL at the price I paid for it. . . net cost= zero dollars
Last year I bought a rear tine garden tiller for 75 bucks, put a start clutch on it (25 bucks), tilled two gardens, and then re-sold it for 250 bucks