Some good news. I'm owning now a wonderful Yamaha S90-keyboard. Such keyboards have 3 PLG slots and can be found on the second hands market for around 500 Euro. The other solution would have been to buy a 2nd hands MU2000.
Soon I will stuff 3 PLG100VL cards into the S90 slots so I can develop VL-Wizard features for MultiPart VL support.
PLG100VL cards have the same features as the PLG150VL cards except that they have no custom slot storage. On average a PLG100VL is about 100Euro cheaper versus the PLG150VL card found on the second hands market. Currently you can still get them between 120-160 Euro while the PLG150VL hits easily around 250Euro.