I have a 1997 Celica ST205 that has what appears to be an OEM Toyota power / keyless remote (single key w/ lock+unlock buttons on it). I have a 1997 Soarer as well, but sadly it does not have the same setup.

Curious on a few things...

1. Was the 1997 SC equipped w/ Immobilizer / anti-theft? (Assuming Soarer was the same).
2. Is there a factory module / option for supporting a remote?

Would rather not go after-market if I can avoid it.

 

The 1997 SC is equipped with anti-theft.
It does not have the immobilizer, that started with the 1998-00 SCs with VVTI motors.

The 1997 SC300 has:
* Theft Deterrent and Door Lock ECU (behind driver side dash panels, higher up under the dash
* Wireless Door Lock ECU (behind the passenger side rear interior side panel - opposite side of Fuelpump ECU)
* Key Fob remote with lock, unlock, trunk, and panic buttons

Now the Key Fob communicates to the Wireless Door Lock ECU, and that is wired to the anti-theft ECU. In theory one can remove this ecu and the car will still have working anti-theft ecu and working power locks.

I am not to familiar with 97 Soarers, but I would bet you probably have the same anti-theft / door lock ecu. But that might be it. You would have to ask other Soarer owners if their cars ever came with remote fobs, or if they ever took the rear panels out and found a an unused wire harness plug.
If you have the plug, it is possible that adding the Wireless door ecu can be as simple as plug and play (or you need to re-arrange a few wires).