actually i have no idea how much it all costs and that's good cuz if i don't know the wife doesn't know! it's been a work in progress since about 1995
probably the most expensive parts of the system (aside from the wiring in the walls and pcs - all of which are refurb or home built or free) would be the jds timecommander+ which was about $700ish back in 95. the IR expander which connects to the tc+ was about $200. starCOM software cost about $100. i don't have any fancy x10 switches, just the standard x10 brand toggle switches. i have some leviton appliance type switches but i got those 2nd hand from a guy over on cocoontech.com who upgraded to insteon. in fact, most everything i buy, i get from ebay or another automation junkie or on clearance. i got hal deluxe for $7 @ lowes
the rio receivers from ebay. slimp3s on clearance. squeezebox on craigslist for $35. i use a wgl800 (20 or 30 bucks) to receive the x10 rf signals and buy the x10 motion sensors and alarm sensors (not for alarm use!) off ebay or when x10 has their 10 for $x deals. 3com audreys from ebay & another cocoontech user. xantech IR stuff from ebay. all the ir emitters from a local electronic surplus store (i paid $1 for dual headed emitters) i use a lot of free software (xAP, xPL) and write a bunch of scripts to tie everything together.
it seems like it costs a lot, but i'm cheap
and it's been over the course of more than 10 years now