It may partly be the result of many people in society becoming wiser about their finances, but the once-proud tradition of athletes paying a teammate to obtain a uniform number seems to be vanishing. The practice used to be so common in pro sports that there was an even an infamous 2005 NFL lawsuit between ex-Washington teammates Ifeanyi Ohalete and Clinton Portis, over $40,000 Ohalete claimed Portis had not fully paid to acquire Redskins jersey No. 26 (it’s a long story, if you wish to Google it).
In the NBA, a relatively recent rule requires players to notify the league of a number change more than a year in advance, perhaps another reason the “digits for cash” market has dried up considerably.