Howdy
Cheapest I've seen a pair for in the UK is £1050. Average is around £1250.
I've been using them for 12 months now and they really pack a surprising punch.
Only last week I was doing a wedding and checkign the sound from the back of the function room, and they easily sounded as good, if not better than my older system that had base bins.
If you suffer from serious DJ penis envy, you migh wish to consider getting the mackie Active Base bin too, just for a rounder sound, but in the majority of cases, you won't need it.
There is an apparent issue with overheating if driven hard, however I've never had to drive them hard enough to overheat them. they have an auto cut off system if over heating is going to happen. this has only ever kicked in once for me, but the room was extraordinarily hot and badly ventilated.
I am considering investing in some powered base bins next year so I can take on larger venues, but will put it off for as long as I can, as cash is tight at the moment

Also, for active cabs they're surprisingly not that weighty, about 21kg, or erm...erm...where's me calculator...ah work it out yourself.
I know several live artists that use srm450's also and they wouldn't be without them now, and same goes for me.
Hope that answers your question.
Darren