Yes, really it comes down to supply and demand, for instance: Only a few companies (3 or 4) reproduce good greman uniforms, so they set the price, Usualy around $500. Where as they made so many Commonwealth P-37 Webbing sets (the fieldgear kit, harness, pack, etc.) and they still produced them into the '50s so they are cheap, around $40. Same thing with weapons and vehicles, A good WWII Jeep will run you around $5000-8000, while a Kubelwagen will run you Around $15000-20000. I have only seen two or three Bren Carriers In the states so they are really expensive, here. You could probibly find a cheep one since you live Down under.
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"Victory at any Price!"
SS-Panzergrenadier