That's one of the problems involved in measuring everything in KT
Take a look at the projected retrofit cost; just before you click to select the design you are retrofitting to, look to the right, and you will see the price in each resource.
Note that you need to have the resources in storage.
Even if you are generating a 200,000 resource surplus, if you've only got 50,000 storage, you can't do a retrofit that costs 60,000 in any one resource.