Deciding when it's "worth it"
Remember that just like return on investment has to define both "return" and "investment" are, the idea of whether or not you're paying "too much" requires defining a couple of variables. This becomes important not only in self-promotion, but also in running your writing business and determining how you use your time.
For an example, we'll use a dog kennel. Specifically, the one I got J-Dog.
Unlike L-Dog, fireworks drive her crazy. This last year the fourth of July fell on a Monday. I had people setting off fireworks from Friday night on. She tried to hide under my desk, under my legs, and behind a recliner. The last (knocking down a floor lamp in the process) was it.
She had to get a better kennel. Kennels are supposed to help dogs by providing a "cave-like" atmosphere. J-Dog's kennel was a wire one with no walls. She much preferred L-Dog's, but he was busy using his own.
So I searched. Second store I went to, there was a near-perfect match to L-Dog's kennel. I bought it, and because the wheels were missing, I got a ten percent discount. I later found a little bit of (unimportant) damage. I probably should have gotten a twenty five percent discount. It was an item old enough it wasn't in the system that was missing parts and had a break in the wall.
I'm still happy.
Even thought I might have been annoyed - that would have been a sizeable chunk of change - I chose to be happy about my deal. It was a seller's market - that means I was probably going to buy the kennel regardless. They got what they wanted - and so did I.
That's the kind of decision you have to make. Don't let yourself get ripped off, but at the same time, don't hold yourself back because of a "might be" that isn't actually there.