The ICOM M421 is the only other ICOM radio with built in DSC, I believe. (I'm sure Superradioman will correct me if I'm wrong!) It is cheaper (around £200 ex VAT) but is smaller so may not fit in the hole without the addition of a blanking plate. Here are some details: http://www.yachtinguniverse.com/shop/page13.htm
. Not necessarily the cheapest place to buy though - just the first one I found on Google!
Alternatively, the M401 can be upgraded to DSC with a separate controller.