What model router do you have?
And why are you looking to buy it?
If it was given free, it is yours to use as long as you have the service.
If you are going to drop FIOS, there are better routers out there to purchase.
Am I right in my understanding that to buy the router, that I have had for the last two years, I have to still buy it for $209?
Unfortunately yes that is the way its done.
however if you are paying a $12 rental fee each month that $144 a year every year so $288 after two years and so forth. You could purchased your own better router like an asus or netgear or TP Link for a set price, return that crappy Fios Quantum Gateway Router G1100 and save money. https://www.dslreports.com/faq/verizonfios?
Under section 3.0 there are instructions on setting it up with or without tv. But if you dont have tv a simple switch to ethernet on your service hooked into your own bought router is quick and painless.
if you have fios tv just get rid of it and buy a cheaper streaming service. Its tv and phone that increase your monthly invoice. Without its a cheaper price.