There are lots of very affordable 1920s vintage dresses on ebay just a matter of your wife searching through them and finding one that she likes. Men's suits none at the mo on the bay a couple on etsy in the 2 to 3 hundred dollar range.....
Fortunately the style of men's suits don't really change all that much and you could perhaps find an old wool at a thrift shop and have someone alter it to a more 1920's silhouette. Would definitely need a vest with it. Add a straw boater or a newsboy cap......
Oh, wait, I just now see you say NEXT THURSDAY----Try to find a rental place near you, or a vintage clothing store.....other than that the best I can offer is hit the thrift stores and see what you can find to quickly alter into reasonable facsimiles........you can do a lot if you were to just keep something modern very simple in color and style and depend on elements from the neck up to carry the 20s theme for you. As I suggested a straw boater or newsboy cap for the gent, one of those stiffened Edwardian collars, alter a tie to the correct shape for the era.
And for the lady a simple clingy shift dress, some long beads or lots of beads and/or a boa, or beads and a detached fur collar, finger curl her hair or if not possible due to present hair style and cut, a felt or knit hat that would pass for a cloche, pulled down to the top of the eyebrows that was the 20s style, dark lipstick......
Good luck with this project. It would have been much easier if you had started sooner!!!
Shylaah