It took almost 5 years for our organization to move off Lotus Notes and that was a concerted effort with a considerably smaller foot print. We had a handful of full-time Notes developers and administrators on staff and were still paying quite a bit in support from IBM annually.

This is a bargain by comparison.

Lotus Notes is incredibly reliable so if the department is just maintaining the system as is, without upgrades or changes, while developing a new replacement solution then a single administrator is probably more than what's needed.