The next best approach is to use a modem in place of a TNC. This approach is about two decade old now, and allows you to operate as a terminal station. It grants you full access to the digital network. And it can support all the automatic digital modes at a much lower cost. There are three main approaches here.
You can buy a commercial modem. The cost is under
$ 100. You may be able to find certain used modems, again at hamfests or on the internet. The cost of these units is lunch money. Finally, if you want, the information is available on building your own modem. It is really relatively simple, and there are no critical circuits. Let me add a foot note here: The commercial modems do not appear to support HF Pactor. Of the used modems, the AEA CP-100 will support HF Pactor with the DOS program “TERMAN93”. You can also build a “TOR Mode” modem.