Is there a 'minimum value' for 1 letter domains with a 2 letter TLD?

[demaxxus]

I may be able to get some single letter domains (with a 2 letter TLD), and I was wondering if there was some sort of a 'minimum value' on domains like this? For example, if the domains were going to cost me $2,200 each, would it be a no-brainer to purchase them because I'd easily be able to sell them for more then that?

I've heard some people say that domains like this are easily worth low-to-mid $xx,xxx because they're so rare, but is that the case?