You wrote "the new US aegis guided missile destroyers... cost about US$1.8 billion apiece."

The US's current guided missile destroyer build programme (DDG-51s) are budgeted at 3- $4 billion each: 
https://fas.org/sgp/crs/weapons/RL32109.pdf 
https://www.gao.gov/products/GAO-16-613 
http://www.defenseindustrydaily.com/adding-arleigh-burkes-northrop-grumman-underway-06007/ :
"flight III destroyers with the new AMDR radar and hybrid propulsion drives could cost $3- 4 billion each"

DDG-51s would provide the RCN with legitimately 21st-century-capable, multi-mission surface combatants, something that surely won't be the case if Canada insists on re-inventing the wheel, & continues plans to domestically design & build its replacement Destroyers and Frigates.

And, most importantly, DDG-51s (version 4s) would enable RCN surface vessels to, for a change, provide legitimate, meaningful contributions to NATO & other allies' missions world wide, instead of continuing to be severe liabilities...