For extremely cheap items, the deputy service at 
Hobby Shop K is probably the least expensive. 
(Closed right now for AX, but likely back soon.)

http://www.hobbyshopk.com/

But like any deputy service transaction, picking 
the best one is easiest by just doing the math 
yourself, with the deputy's other services taken 
into consideration.

When I buy "little stuff" I usually just wait 
until I can combo it in with other cels.

Many Sharp Smiles,
--Drac