$300 included machining a part needed to charge the cartridge.
Normal service is around $125-150 depending on parts.
I seem to remember my WP forks being around $90 or so.
The extra $$$ is most likely because of the cartridge design.
The Traxxion forks would be around the same as the WP forks and need service yearly as well, so I guess I'm missing the point.
I'm guessing you don't service your suspension. Or do you do it yourself?