To answer your second question first - each renewal is treated as a new application and the paperwork is the same each time.
Additional cost would include photos, translation of documents such as passport.
It then depends if you get an agent to do it for you (easiest) or do it yourself (not easy). The cost of an agent doing it for you starts around 200ytl and goes up depending on how fast you want it completed - in Fethiye, for example, that would include the agent either doing it snail-mail or, at the top end, physically taking the papers up to the regional centre in Mugla. I think the top rate was around 800ytl last year - not sure of current rate or what your local position is.
There is ONE cost which isn't payable every time - the residents permit book itself. I think it's about 70 YTL and once you've got one, it can just be restamped and amended (unless it falls apart like mine).
By the way it might be different in different parts of the country but I didn't need to get my passport translated. Just took that (and my tapu) to the Emniyet Muduru or security chief in Aydin (the nearest administrative centre to Didim that handles first-time applications).
At the E.M I was given a form to complete (in English), submitted my paperwork and photos and was given a ticket to take to the tax office. At the tax office, paid the amount on the ticket and was given a receipt to bring back to the E.M. where it was added to my file.
Then I was sent away to return a week later to pick up my permit.
So actually it's not that difficult, but if you're easily daunted take a turkish-speaking friend with you so you can understand what's going on and where to find the tax office!
We just renewed my husband's residence permit and did the round - passport police, kaymakam, town police, photocopy, tax office, another office for the information to be put on computer (Captain something or other opposite the passport police) and back to passport police in just one hour.