I set thresh-hold by series based on what I 
perceive to be the average market prices at the 
time (and review them). I will spend on a cel 
within the price tresh-hold for that series.

For instance for GTO cels I will not spend over 
$50.00. 

But for say Cowboy Bebop Cels $500.00 is the 
limit I will spend per cel.

I have not decided on any upper limit but 
realistically a price beyond USD1,500.00 would 
start being irrational - for me. (But that's just 
me)