Pretty easy, if you have the time to go to the thrift store more than once--they rotate their stock quickly and if they don't have what you need the first time, keep looking.
Useful things: one long skirt and a tablecloth or curtain in a color/fabric/print you like. Wear the skirt underneath and use knots, safety pins, or quick stitches to gather the overskirt (tablecloth) into a poofy bustle. Freestyle; there's no wrong way to do it. This is also an incredibly easy bustle skirt from scratch
For the top: I get a lot of mileage out of a black velvet jacket of the sort that always seems to come out in stores around this time of year (not exactly upscale, either, mine's from Old Navy) and a regular white dress shirt, both with the collars turned up. Use a narrow scarf as a cravat and pin it at the throat with a brooch. Tuck the scarf's loose ends into the front of the jacket. It's a nice antique look. A vest under the jacket is also great, especially if the jacket doesn't button very high.
Shoes: sometimes you get lucky and there's a pair of granny boots. If not, any simple flats are fine.
I love me some thrift-Vic.
Good luck at the shops.