dicer

It is easy enough you can do it. And you don't need "Top hats" they are covers for the air suspension control motors, that is if its like the ones I'm familiar with.
You can do it your self for around $800 or so, maybe cheaper on ebay.
http://www.strutmasters.com/suspension-parts/lexus/
This is all pretty much bolt in you jack it up and use something like this to separate the upper control arm ball joint from the knuckle assembly. And if the struts and springs are an assembly out of the box its just the 3 tower nuts on top and one large bolt and nut on the bottom and maybe a few other things to get out of the way so it all lowers enough to get the strut out and new one in.

And yeah a bit more involved if you have to get all parts separate, its best to get them all assembled and ready to install. You can watch videos on youtube that will show how to. It really isn't a super difficult job and not one to pay a huge shop bill on. The hardest part is jacking the car and setting it on blocks or jack stands.

semar

Now that we have the airsuspension off (nothing difficult) here are the parts needed to convert to coilover
Front
Struttop 48680-50110
Big top washer 48680-22050
Rear
Rubber insulator for spring 48258-50020
Big rubber insulator 48257-50020
Bumpstop 48341-50070
Strut top 48755-50100
Big top washer 48755-50110

All parts x 2 (for left and right)
plus struts and coils or complete coilover system
The parts from the airsuspension will NOT fit a straight coilover change