http://www.mosis.com/prices.htmlheres a waffer pool, they gather lots of designs from all around and put them all on one wafer, it makes developing your chip a lot more affordable, to know how cheap you need to know how large your chip is going to be and what technology you plan on using then you can get a quote from them, eventual implementation in asic might be economically feasible in a year or so if the bitcoin economy grows at a current rate and trasaction fees start bringing money in. but first the technology must be optimized and verified on fpga before anyone will even seriously think of paying all that money for trying the design out on a asic
if bitcoin grows eventually asic implementation will be more efficient than using graphics cards and the first one to come up with an asic design for it will make some neat profit. i hope there will be an open source implementation but probably some corporation is going to cut in and steal that low hanging fruit if it becomes profitable enough, right now its far from profitable enough