A.  I believe there was a thread on this forum
    stating that the plastic boxes cost $1-$2.
    I'm in the USA and can get them from an
    import shop for $2.

B.  The seller specifically said, "please do not
    use airmail."  It seems rude to send via
    regular mail when he specifically asks you
    not to.  Who knows, perhaps he will be less
    inclined to deal with you in the future.

C.  I guess if you don't have paypal, then going
    through the seller may be a better option.
    But what do you mean by:
    
 Also, not everyone uses paypal or has that 
much money to pay Celga in advance.

If you're willing to pay $X for something, 
shouldn't you have the cash to back it up?  
Whether celga is holding a deposit for you, or 
you're just waiting to hear if you've won, you're 
still committed to the bid.  If the cash is 
earmarked for something, why would you be 
spending it on something else in the meantime?  
(And please don't say "for an emergency."  If you 
don't have some spare cash for an emergency, you 
shouldn't be committing the money to cel 
purchases.)

Sorry to go off on a tangent.  My point is, for 
bids under 10000yen, the cost-difference between 
bidding via celga and bidding directly with the 
dealer is nominal.