Low cost is pretty subjective. There are lots of factors to consider like what purpose you want to use the car for, emission legality, street legality, local market prices, how much work you can do yourself, luck, etc. You don't need to do a full on pro touring build to enjoy a classic car, despite what the marketers say.
G bodies are antiques and require a sh*t ton of upgrades to begin to approch modern standards of performance. But you can never make a antique fully modern and kind of defeats the purpose of owning an antique in the first place. Even back when they were new they were never designed to be sports cars. The original designers ruthlessly sacrificed performance for comfort and utility. Still they can be greatly improved upon without getting caught in keeping up with the Jones syndrome that many hotrodders fall for.