Yeah, I've had to check into these prices before for a potential client. Lets just say you don't even want to know! 457nm is good for higher end projectors, but they're also even more expensive than 473nm
I have a 3W green version. Some of the blues appeared on ebay a few years back when they were still made. All were broken and hardly a bargain was found.
There are already 457nm diodes, but I doubt that they can even make powerful ones without cost-prohibitive cooling (wild guess), 457nm diodes are used for media reading purposes.
457nm is a more real blue anyway, while 473nm is more a "cyan-ish-royal-blue" color.
My company offers much higher power systems but advertise only up to about 1000mW because nobody...I mean nobody purchases high power blue with only a very few exceptions and these are built on order. You will not find a 7+ Watt blue unit available for overnight shipping...not even from the manufacturers because that is a major risk to have sitting on a shelf waiting and watching the price fall over time.
Blue is very nice to look at but exceedingly expensive to purchase for lab use since not only do you pay a premium for the laser but optics AR coated or designed specifically for 473 or 457nm is much more expensive than those specific to 532, 1064nm.
We have sold blue systems but they tend to congregate in the imaging industry as opposed to the laboratory.
For the price of a 7W blue you could purchase an 80-100W green DPSS system. You'd get a more powerful laser if you went with an arc lamp pumped industrial system for the same price.