A decent scope ?
What do you mean by "decent"? What magnification? What purpose? What platform will you mount it on.
You know more about unicycles than I could imagine there is to know so you have to understand you have to know enough to tell us the applications?
Red dots? Put this on an AR https://www.aimpoint.com/product/aimpoint-compm4/
ARs? Entry start at the Aero Precisions https://www.aeroprecisionusa.com/m4e1-complete-rifle-16in-223-wylde-mid
Handguns? That's much more challenging since I think you need to find out what points naturally for you before buying a handgun so you're getting what fits you and not the next guy. How much for "decent"? Decent can start around $500 for new and go up.