Because I do mostly custom work, this gets a little complicated...The best I can do here is give you some ballpark ideas. For an exact price, just e-mail me and I'll get back to you real quick.
Price ranges for various items are usually like below:
Braided Chokers w/standard buckle - $20
The "Black Widow" w/standard buckle (picture DC1) - generally $50
The "Torture Collar" (picture DS5) - generally $75
collars - single layer of straight cut leather, ring, locking buckle w/padlock - $30-40
collars - two layers of leather (1 inch over 1+1/2 inch for instance), ring, locking buckle - $40-$50
for instance, the collar in picture DS1 hanging ring plus two D-Rings is typically $45
posture collars - single layer of leather, Vee or other shape, ring, locking buckle w/padlock $35-$50
add braided edges to a collar - add $30-40 to price (braiding takes a couple of hours per foot to do!)
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A few things that can affect price further:
additional rings or fancy types of rings - rings can typically be $1 to $5 additional per ring, and fancy rings can typicaly add up to $5 additional.
diamond studs, chains, etc - very dependant on the collar.... please ask
spikes can range from $1 each for 1 1/4 inch spikes up to $20 each for the big 3 inch aluminum ones
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Shipping - shipping is done by Priority Mail, and will run $5 for many items, up to a few dollars more for heavy items (continental US Destinations only)
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I think my pricing is fair for the level of quality you are getting. It takes quite a bit of time to make stuff right :-)