growth over the cost base which would be purchase price + holding costs is what i'd be using to figure out ROI
Example 2k holding costs, 5k funds used (7k investment). Purchase price 100k
100k + holding cost 2k = 102k + say growth of 5% on the orginal 100k which is 105k. 105k minus 102k = 3k profit.
3k divide by 7k (invested money) = 42.8% ROI over a 1yr period