When to repair or replace speakers?

So here is the situation folks, I have a pair of Polk RT2000P speakers that I have been using for 9-10 years (bought used from this site so maybe 15-years old). Recently I hear a thumping / knocking sound of the left speaker sub when under normal listening levels when heavy bass is present in a movie. I think the surround may have given out allowing one of the powered 8" drivers to bottom out but I am not sure. It has happened a few times so I don't think it is a fluke but i dont see sny physical damage to the cones or the surrounds..i am considering getting them re-coned but since there are two drivers per cabinet and two cabinets, I am looking at 4 cones and I am not sure that this will be cost effective. This also assumes that I have ID'd the problem correctly and that it is not power related with the built in amp throwing too much juice.

That said, I know that at one time these speakers were around $1k each and well regarded. I have to assume that to replace with something new and equal or better quality I am in the same price range (maybe more if I need to buy a separate sub). If I look for replacement / upgrades what price range am I in now and what do you recommend?

How much should I expect for the repair bill on them with the issue I described?

I am running an Integra Audio DTR 40.1 reciever and I use this setup for movies and CD listening through a Marantz CC4003 changer with a Polk CS400 center speaker.