seems simple enough if I'm understanding it correctly. One question though: is total cost simply the one value corresponding to the year the alternative starts? or is it that year plus all subsequent years?

If the former, then in your example would the correct solution be Alt1: 2013, Alt2: 2013, Alt3: 2014?

(total cost = B2 + B3 + C4 = 23 + 0 + 0 = 23)

or if the latter, would the correct solution be Alt1: 2017, Alt2: 2016, Alt3: 2017?

(total cost = F2 + E3 + F3 + F4 = 41 + 32 + 42 + 43 = 158)

If the former, then in your example would the correct solution be Alt1: 2013, Alt2: 2013, Alt3: 2014?

(total cost = B2 + B3 + C4 = 23 + 0 + 0 = 23)

or if the latter, would the correct solution be Alt1: 2017, Alt2: 2016, Alt3: 2017?

(total cost = F2 + E3 + F3 + F4 = 41 + 32 + 42 + 43 = 158)