Where are you based and do you suffer from much bike theft?
A documentary her ein the UK called 'Gone in 60 seconds' proved matter how much you spend on a bike lock they can cut through even the most expensive ones in under a minute anyway with proper bolt croppers or cable cutters. I'd say don't buy anything too heavy just a reasonable U lock as a deterrent, just make sure it has good reach. Chains are more flexible but tend to be heavier if they are any decent density and length.
I think this snowmobile all purpose lock on eBay is a steal for you:
http://cgi.ebay.com/ebaymotors/THE-C...spagenameZWDVW