Recommended transmission for a commuting bike
New you can't do it for less than $200 unless it is off brand (not Shimano or SRAM)

Shimano does not offer 1x11 in the lower end groups.

It would be like 1/2 the value of your bike.

Not using the smallest up front is not a big deal.  I would just keep what you have.  

You can remove the smallest and adjust the range if you want to.

Or you could swap to double crank.  Not sure if you can still use the same shifter or front derailleur.

Not seeing many used 1x11 yet.  Maybe look for a used 1x9.  I don't think there are any true (narrow wide) 1x8.