Probably more than $500 though. http://www.unionspecial.com/wp-content/uploads/2200M18-10-31-13.pdf Looks to be similar to bag sewing machines used for seed and feed bags. Have any elevators or feed mills around that sew bags where you could borrow their machine or get someone to run a seam or two ? Probably need to run a nylon heavier thread instead of what they use to sew seed and feed bags. Then there is a consumer style machine. Lower cost but may not work with tarp material but at least your not out as much money if it does not work. https://www.target.com/p/singer-handheld-sewing-machine-white/-/A-51920449 | 
Hand held sewing machine for tarp repair.
