ROI in this case is not relevant imo. You are not investing the 1000 DASH, you do not give your 1000 DASH to anybody else, you maintain them in your own wallet. Compare it to a savings account that earns interest.
Buying 1000 DASH for one masternode cost you 14.000 USD right now. You earn over 100 USD per month with one masternode, that is 1.200 USD per year. The current interest rate is 9.48% annually.
Remember you can spend your 1000 DASH within seconds at any time and sell them.
DASH price is likely to go up as well. For example when I bought DASH a few months ago it cost 7 USD per DASH, so I also doubled the USD if I was to sell all my DASH right now.