Some years ago I took on the task of creating vintage costumes for a "cast of thousands" with a budget of $350. Even though I had real vintage pieces in my personal collection and the theatre had some actual vintage pieces, there was no way authentic pieces could withstand the rigor and flurry that goes on backstage, never mind what strenuous action may be required onstage.
My adventure to find over 500 individual costume pieces that could go through the quick changes and shameless neglect of actors took me far afield. There wasn't a thrift store within 200 miles that I didn't explore. As I examined books and photos of vintage/antique clothing, I learned how to take a basic modern garment and by "cutting and pasting" from one garment to another, I could achieve the "look" of vintage without paying very much for each piece. From shoes to hats to skirts to pants, the 500 pieces came together within 6 weeks and almost exactly in budget. A lace collar from an 80's modern dress went on a black blouse with full sleeves from the 80's. Small men's trousers were cut off and became knickers for pre-teen boys. A woman's wide brim summer straw hat was spray painted black and heavily trimmed with bits and pieces from other modern clothing.
It was one of the most enjoyable challenges I ever had as a professional costumer. Sometimes it isn't what you spend, but what you create for a pittance that makes showtime "vintage" so much fun. Of course, in real life, real vintage is so theatrical!