Besides, where in your calculations is the RESIDUAL value for the miner?
It was ~55% in BTC and 35% in $$ for SP30 after 12 mo and 53% of SP20 in $$ and astonishing 78% in btc after 10.5 mo (even with a high price paid for SP20 before discount to $400-500).
Avalon sadly is not Spondoolies or Bitmain when it comes to demand in the used miner market but depending on how successful you're with timing your exit (the 3-month contract renewals might complicate that) you should be able to get 20-30% back after 6 to 9 months.
Unfortunately that part is even less predictable than difficulty/exchange rate/etc. Depends a lot on what other hardware is available at that time.