TJ Says he's underrated and I agree:
https://www.yahoo.com/sports/t-j-houshmandzadeh-says-bengals-033048677.html
He'll be less expensive than Tee, not by a ton, but his #'s aren't so gaudy that he won't be affordable, unless some team just gets stupid (entirely possible).
When I look back at all the highlights from the last 2-3 years, Boyd is everywhere, always making a huge 3rd down play or tough catch when they needed it, big TD's etc.., I don't know how they replace what is probably the best slot WR in the league. But, the Bengals' won't pay all 3.
I'd be tempted to approach him and Tee and extend whomever is most affordable/realistic, and find out (if they haven't). If Tee wants #1 money, I pay Boyd instead if he's reasonable and wants to stay, for instance. Don't want to lose 2 of the 3 either.