Fees for radiographs (x-rays) may vary depending on where you live or where your dentist is located (area of country, urban, suburban, center of town, etc.). In addition there are always going to be a range of fees for the same service. Also, the fee will vary according to what type of radiograph(s) you need for diagnosis of your oral health. You may need a single periapical radiograph, bite-wing or "cavity detecting" radiographs, a complete mouth series, a panograph or any number of other types of radiographic films or studies.
You may be able to find average fees for dental treatment in your area, but as with most other things just because a product or service may be the cheapest, does not necessarily mean it is the best. Also, you must feel confident in the dentist providing your care.