I've done a bunch of bike seats. About $15 for black naugahyde at Jo Ann fabrics. Pneumatic staple gun is a must. I found it impossible to use a hammer to seat the staples from a normal spring gun
The trick to getting the corners right is to make very small tucks and use lots of staples oriented on the radius of the corner.
UncleWray's Motorcycle Painting & Upholstery
Our Motto: "If it looks real bad from a mile away, you know you came to UncleWray"
Our Guar-ron-tee: "If it doesn't look bad from a mile away, we'll drive you closer till it does!"