X-ray costs really depend on several variables - you might need to include a few more details to obtain a more accurate guesstimate. 

1.) What are the part configurations, sizes, and code requirements? 

2.) Do you need to measure and track the individual defect sizes, or is it a pass/fail inspection? 

3.) Do you need a code stamped and published disposition report by a certified (level I, II, or III) inspector, or will you or your staff interpret the results yourselves?

In my own limited experience, I seem to recall a 4 hour minimum or minimum overhead charge - but we had our parts shipped out to the NDT shop.  They did provide mobile service as well, but our needs were better served by using their messenger pick-up and return service since our parts were small.

Our own costs for tube weld radiography ranged between $10 and $40+ per shot - depending on quantity and complexity of the report(s).

$45 to $65 per hour might not be uncommon for a level III NDT reports, but, sometimes they will quote you a flat rate.  The more complicated the code requirements and report publication needs - the greater the expense.  Please seek the advice of others since I have been "out of the (X-ray) loop" for more than 5 years now.

I don't know your location, but you might want to check into GE Inspection Services.  They are a top flight organization, and offer excellent service at a reasonable price - I had better stop now, because we are supposed to keep the forum "non- commercial".

We pay a 4 hour minimum plus $1.25/ mile and that's just to start. I believe that we are paying anywhere between $60 and  $125 per hour depending on whether it's a scheduled shoot or a last minute oops...we forgot that we need that joint shot type of deal. Also it's all dependant on whether it's the weekend, after hours (after 1700hrs) and of course they really get ya if it's Sunday. Just as was said By OBEWAN though it all depends on where you are and how much competition is out there for the work.

Yes, I agree, it depends on the level of local competition - and also on the workload at the provider.  Sometimes they might charge a hefty expediting fee for high priority work.

And, my figures are probably low relative to some of the more complicated inspection needs.  I also recall $85 an hour for detailed lab reports...and, some shops might charge over $100 an hour and upwards...

The figures I recall were for very simple, easy to complete tasks that did not involve mobile labs..

Depends on many factors such as competition, distance to their office and a myriad of other factors.
If memory serves me correctly, a year and a half ago, I was paying $500 for a 4hr minimum. This was using a BIG name firm that was 10 miles from their office and on the border of Houston/Pasadena.
Which incidently was the same figure we paid back in 2010 on a more remote location in Wyoming with a somewhat smaller firm and 130 miles from their office. But out west, these RT crews live "On the Road" and in their trucks. This particular crew was amazing though. It was a Power plant boiler and after hours shoot with no elevator. The Level II tech had once qualified for the Olympics in Track and Field events. I never seen a fella that could/would RUN up 250' of stairs with cables and a camera in hand. We could get 10 - 12 hours worth of shots from this crew in 6 hours.