I too found Kia pheonix about the dearest for Kia servicing. I challenged the service guy about this amount which was £200 for a my 4 year oldRio diesel 24,000miles service to Kias recommendations. He said they could do a Pheonix service for £125 due to my warranty ending after 3 years. This service was basiclly a oil/filter change and check and adjust a few things as the previous 3 year 20,000miles service included a fuel filter.
If yours is still under warranty you can still take it to a non dealer garage as long as you use Kia parts.