Off the shelf..... 129.99
But can be built better:
Strap - 36" grade 1 leather 1/2 x 1/8 $24.00
Material - 4 Sq. Ft. 3/16" leather $38.50
Thread - 1 spool, Carpet grade $8.25
If you've never built your own purse, there are plenty of very knowledgeable guys here that have either done their own, or build them for a living, and they can give you plenty of advice and hints.