A good active crossover will run anywhere from $1,000 to $4,000. You don't want to skimp on the crossover because _everything_ in your system will be going thru it. You will be adding another link to the chain on the signal path so you want to take care that the link is "pure" and doesn't take away more than it benefits. _Everything_ you put in the signal path will have some effect, so you want as high a quality crossover as is comparable to the quality of the rest of your system.
The active crossover will take care of gain matching and crossover duties.
Generally, one of the major benefits of active bi-amping is better control of the transducers and flatter impedance ( and ensuing flatter response) without the passive crossover components in the signal path.
You did not mention your specific speakers and drivers, and crossover points. I am uncertain as to the benefits you would have from bi-amping your current speakers _grin_ Depending on your configuration it may well not be practical in terms of costs to benefits ratio.
For more on biamping go to AA and search for John C Aussie biamping FAQ
Regards
Ken L