If you're running campaigns on a CPI basis, nothing in the app -- content, IAP prices, ad placements, etc. -- will impact the CPI price you pay. Campaigns that are optimizing for installs are only impacted by 1) performance of ad creatives (CTR) and 2) performance of app store page assets (install rate).
This isn't to say that in-app IAP prices won't impact your ROAS, which they absolutely will: the price you charge for in-app items will define your overall user economics. But CPI-optimized campaigns don't use any in-app behavior to define targeting, so your IAP prices won't impact the prices you pay for installs.