Starter or Ignition switch?
 

Purchased 2005 x5 4.8iS on Saturday. Everything cool in NYC (of course). Drove to NJ/PA line, stopped for gas.

x5 would not start. No crank, no clicks, nothing. Dash lights all looked great. After poppin the hood and checking around jumped in and started up.

Ran fine, stopped near home. Came back 2 hours later, started normal. Drove home and parked. Sunday afternoon, first time tried to start since parking the night before, and..

x5 would not start. No crank, no clicks, nothing. Dash lights all looked great.

I did not bother popping the hood or anything, just came back five minutes later and started right up.

Started multiple other times that day with no issues.

Sounds 90% like what happened to mine not too long ago.it was the ignition switch.

What's worse in terms of costs, starter or ignition switch?

Mine is doing it as we type here. I've researched and found an article on how to take the switch apart and clean it for free. $39 to 89 for a new switch.
Part# 61 32 6 901 962. Make sure its the right part for your car.

Ignition Switch Rebuild DIY

DavidClass, are you in the process of rebuilding yours now?

Nope, just had back surgery and not ready to wrestle with the steering column. I might on Saturday if I can lean forward enough. I did drive it last night though, and miss it alot. It wouldn't start again(after it started 4 times in a row). I got it washed so its pretty and not running now.

I took the switch out tonight and studied it for a moment. There are 6 contact points that open and close to let power through. The red wires in the middle of the switch are always hot. The big green wire is the culprit. When you turn on the key, the green goes hot and it will start. When you turn the key on and the green stays dead, its not going to start. Its that contact that apparently gets.... whatever they get, and won't actually contact.
So I took it out and fabbed a metal finger nail file on the grinder so I could get it between the contacts. I lightly filed each of the 6 contacts and put it back together. There are 6 tabs you pry out with about 4 hands and 2 screwdrivers to pop the top off the switch.
CHECK THE ORIENTATION of the cam that opens and closes the contacts and mark with a sharpie and don't let the cam come off the plastic base plate. Its ok if it does, just pay attention to how it goes back on.
So far, about 10 starts in a row without issue. Going to drive to work tomorrow and see if I get stranded.
DO NOT take out the little red painted set screws that hold the switch in place. Just loosen them as they are small and a royal pita.. whoops I said royal... go royals, bases loaded no outs!!! Anyway they are difficult to get back in.
The biggest bitch is the plastic retainer around the switch itself. Two #30 torx screws hold the cover on. To get one of them out, you have to use just a tip and 1/4 inch wrench.
Also need to cut the plastic wire ties to loosen the wire bundles.
Damn, 7 runs this inning!!!

Wow, nice write up DavidClass. Hope you don't get stranded.

I have mine at my mechanics now, needs an inspection, emmisions and the ignition switch by the sounds of it.

So here is what's up with my x5. Mechanic had it start every time. One time while exiting driver seat, hit gas pedal. Dash went dead and radio off. Hooked up scanner for codes and got an "Instrument Panel" fault. Cleared codes and fault came back. Dash and radio fully operational now.

Anyone have an issue like this?

Could be a glitch in the scanner or software if you are using a laptop.
What are you using to scan the X? Should go to Bimmerforums and look at the Diagnostic forum, or post your question there. There are more knowledgeable people over there when it comes to diagnostic software.