Providing a "hardware-only" solution would be a wise move. Seriously cuts the true cost of the product. Expanding to large numbers of I/O is very advantageous, often during design of equipment you end up in a debate of culling the herd of data to a limited number of ports.
Your price does sound good. Access I/O does have lower priced cards, stuff like this: **broken link removed**
the product sounds interesting, there is definitly a market for these things, it all comes down to price and functionality.
One thing that comes to mind is the connection interface. Providing space for more than 24 inputs gets demanding, and expensive for cases / PCB area, and terminals. I would suggest a high-density connector, allowing the customer to have one small connection to your device. AMP make numerous high density connectors, like their Multilok series. Another option would be to use ATA style connectors, to ribbon cable. You could offer "break-out" boxes - More product to sell!