It's perfectly ok to buy whatever you can get, 
right? As long as you don't go and harass owners 
of the sketches you search for, it's your choice 
and nothing to do with greed. Things with prices 
on them are meant to be bought, no matter who 
buys them. 
Surely, you'd have more important things to spend 
your money on though, but that's something 
everybody has to decide for themselves. 
It's nothing to do with etiquette when you buy 
something which is for sale (=do what's expected 
to be done).
To me, cels are just another market, like 
everything else you can buy and collect. So, the 
one who buys it is right, no matter how many they 
buy for how much.

Ne^^