If the API is being hit on every page load there is no way to display the page without hitting the API.
As @Steve Ostenmier points out you can embed the conversion data in javascript which Google will still be able to parse but will only result in a single hit to the API if your API supports getting all of the conversion rates in a single request. Either way whatever you do it will require a change to the underlying code driving your site.
A good rule of thumb to follow is anything an end user can do without requiring a password can be done by Google and if it is done will likely be done orders of magnitude greater in a far shorter amount of time than a single or small group of end users can achieve themselves