the cheapest way to is to learn how to tether without the carrier noticing. I use a product called pdanet, which simple leverages the EDGE connectivity and AUTHENTICATION that the device already has.

Since you have a slow data connection on the DASH (although, usuable and about 2x what a dialup modem would offer) you could just use the BLUETOOTH connection for data transportn and internet sharing. Bluetooth has a max thoughput of about 400kps, so when I use my MOGUL which does 1MB download speeds on the sprint EVDO network, I normally use the USB cable to get the full speed of the data connection.