Buying is always the (long term) less expensive option. That said, and in this instance, I'd suggest you go with the rental option and then shop around for a black Argyll jacket and two waistcoats (one 5-button, the other 3-button) in your size, which I'm guessing is probably a 44 Regular (6ft + 190lbs = 44REG). Head into your local JCPenny's Store and try on a few jackets until you find one that fits, then look for that size in an Argyll.

An Argyll is far more versatile than a Prince Charlie coatee as it can be worn for formal day wear, dressy evening wear, and (with the three button waistcoat and black bow tie) for formal evening events as well.