Old English upriht, from up "up" + riht "right." Similar compounds are found in other Germanic languages (cf. Old Frisian upriucht, Middle Dutch oprecht, Old High German ufreht, German aufrecht, Old Norse uprettr). Figurative sense of "good, honest" is first attested 1520s. The noun in the sense of "something standing erect" is from 1742.
THREE-PENNY UPRIGHT. A retailer of love, who, for the sum mentioned, dispenses her favours standing against a wall. ["Dictionary of the Vulgar Tongue," 1811]
The bent-over rear-entry posture they are talking about, of course, is kubda, the three-obol position at the bottom-end of a prostitute's price-range. [James N. Davidson, "Courtesans and Fishcakes: The Consuming Passions of Classical Athens," 1997]