Seems to be the best price I've found online. Haven't checked my local HD or Lowes yet, just getting an idea if this is about the right price range.http://www.amazon.com/gp/product/B002G9TNDS/ref=noref?ie=UTF8&s=hi&psc=1
I think 10/3 SJOOW or SOOW is like $1.85/ft at Home Depot. Basically the same price as that but no shipping time. It may be $1.65/ft. I can't remember.
When I was looking for 10/3 cable, this was the cheapest I could find, and it includes a locking receptacle (if you are using 120V), but I am not sure about the temp rating if that is a concern...http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=330383299611&ssPageNam e=STRK:MEWAX:IT
Maybe this: 25' 240V 30A for $29 free shippinghttp://motors.shop.ebay.com/__?_from=R40&_trksid=m39&_nkw=RV+POWER+LIFE+LINE+C ORD