There is a way to use a RCC like limited Cyberdeck, it's not the most efficient way but it exists. Put a 'Add Sleaze Modification' and 'Increase Sleaze Modification' on your RCC then pick the Practice, Practice, Practice (Hacking) quality. It will gives you a limit of 3 for your Hacking test, you can then add Programs like Exploit, Stealth or Smoke and Mirrors to raise it further.
The cost is still lower than a high end Cyberdeck but you will be limited to one aspect of the decker (either Hacking or Cybercombat).