huh, so WASD does finally have MX Greens...
Basically, two options here: do you want backlighting? If yes, Ducky has the most impressive array of options (colors and switches) as well as functionality.
If no, I would recommend finding a replacement non-ABS keycap set. All WASD keycaps are ABS. Ducky does offer PBT keycaps, but PBT keycap sets for standard 104 ANSI keyboards can be found here. However, if you are seeking MX Greens, you are rather limited.
Backlit MX Green options:
Ducky Shine 3, blue or white $169
Code when it comes out (I am going to guess around $170 for MX Greens)
Normal MX Green options:
Ducky G2Pro MX Green w/ PBT: $144
WASD barebones: $120 + a keycap set
WASD w/ custom ABS keycaps: $170
Cooler Master QFR, Trigger, XT, $100 - 120 IIRC