The most entry level bullpup you could find that can be set up for a lefty would be the Walther G22. It is a 22lr bullpup, and the chargine handle and ejection port can be set up for a right or left handed shooter. I bought mine used for 300 bucks.
Larger caliber bullpups like the FN FS2000 (which I have) and the Keltec RFB eject cases from a port in the front of the firearm, and are totally ambidextrous. They are also very expensive (I paid 1650 for my FS2000, and the RFB is around that, IIRC.).
The FN PS90 i believe is bottom ejecting, so it would work for a lefty, and the Steyr AUG can be set up for a lefty. Both of those are are also expensive.