There are few of us today unaware of the advantages of x-rays. However radiography in the dog tends to be a little more complicated in that you mostly are unable to tell your patient to lie still, turn this way, turn that way, hold your breath etc. Therefore either heavy sedation or a general anaesthetic is usually mandatory. Also, since irresponsibly used x-rays can carry some hazard there are strict health and safety regulations regarding their use.
Consequently, radiographic examination in the dog usually involves an anaesthetic fee. In addition more than one view is necessary for accurate evaluation of a particular region. As a result most radiographic studies require several x-rays.
Finally, the radiographs have to be interpreted and sometimes a specialist veterinary radiologist has to be consulted for this purpose.
All in all therefore the procedure is likely to be more expensive than, say an ECG examination. Your veterinary surgeon will be more than happy to discuss procedures and costs with you.