The way we use today'* cars, making short trips and constantly locking the doors, the cars really must have a remote fob to avoid wearing out pants pockets and keys. I was suggested that 99.997% GM cars come so equipped. I just bought the 0.003 % Buick which is without*. I've added aftermarkets to my other 3 other cars but the Buick is different. Before I learned the car wasn't equipped I bought an used OEM fob from eBay for $20 which I will chalk to lesson learned..

I don't expect to connect all possible features such as horn, lights, auto re-lock after start etc. The door lock-unlock functions by key fob are mandatory, additional whiz-bangs are gravy.

I undertstand the driver'* door panel comes off easy for access to the 'lock'-'unlock' switch should be easy. If I can't find constant +12v in the door I plan to place the body module in the door with dry cells (2 year replacement). This would minimize wiring by using only the existing lock-unlock switch.
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*Attempting the programming setup for a new key fob doesn't provide the correct 3 verifying beeps. PLUS the RCO code AU0 isn't on the paper afixed in the trunk.
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Please advise which you might do differently, better, cheaper, or not at all.