To do the sliding pins is easy. Really, I did mine the other weekend!
There is a guide on here somewhere, do a search, which shows pics and everything.
You may as well buy new pins, dust boots and the bushing (only needed for bottom pins) and try that first.
I also found that my bottom piston was sticking, so temporarily I freed it by clamping it in then pushing it out (with brake pedal with bit of wood to stop other piston moving) and just did that loads.
Fixed it temp. but will renew seals and pins etc soon when get the time/parts.
But seriously, the pins are eaaassssy. If they are really stuck (like one of mine) then you may have to tap them out with a smaller spanner over body of pin against the head of pin end. I had to hit hard as one of mine was mega rusty!!
Mat has kindly posted the Part Nos of the bits in the part number sticky but prices are:-
Dust boot = £3.94 pair
Top slide pin = £5.42
Bottom Slide pin = £7.21
Sliding bushing = £3.07 pair
I don't know why both pins are not made from the same material - think the top is some bronze coated jobby or similar, but the bottom is simple steel and rusts like mad!
For info, the caliper rebuild kit (piston selas, rubber boots and set rings for all of front calipers) is £63.46. A new caliper is £260.
Al prices are ex. VAT and from Lexus.
Oh, and if a piston is really seized and you suspect it may be excessively pitted, then they are £19.29 each. :-)