cheap (inexpensive) prostitute.(obs.) word from Victorian England. threepenny (thrup'ny) was the price, upright was the position (to facilitate speed, therefore rapid turnover of customers), "the deed" was frequently done in alleyways. Known use found in Bertolt Brecht's "The Beggar's Opera".
" 'es got the pox from seeing too many thrup'ny uprights" "A Lady?, Hell, she's naught but a threepenny upright."