I am also tight with money. I used an 18"x12" section of closet rack. I cut the cross wires out of the last 6", bent the ends into hooks and put bolt on the inside holes on the backrest. I install it by putting the ends through the backrest, hooking them onto the bolts and putting bolts through the rear holes to hold it up. After getting it on I strap a rollbag (aka cordura trunk) onto the rack to cover up my redneck rigging. So far I've used it on 2 500+ mile trips packed with a freezer bag, 4 frozen water bottles and 4 refrigerated water bottles and never had a problem. It's worked good and keeps the water cold for about 8 hours.
You'll have t use you imagination cause I'm not posting pictures. Wouldn't want to risk copyright infringment...
Retired USAF, IYAAYAS!
2008 V-Star 1100 Custom Bobber project
2011 Crimson XR with Forged Highway Bars / Hard Bags / Passenger Backrest, Ness parts including Smooth Layback Plate Frame/Mount / Rad 3 Mirror / deep cut grips / drivers floorboards /shifter peg / brake peg / passenger pegs. Witchdoctor black rack, Lloydz filter / timing wheel / VFC III, 7Jurock windshield, Drag Specialties seat.