best sub for spendor s8e and 2500 c feet room?

I use REL Stadium 2 and 3 with my SP-1s and S-100s. Cross them over at 22 Hz and drive them from the speaker terminals. Sounds great.

Think your best bet is a pair of subs in a room that large. Sorry to burst bubble & budget.

You can go with cheap subs if you don't push them to go down into the 20's. Set them to roll off at 36hz +- and they will work fine. Even expensive and big name subs can and often do sound bad at those low frequencies. Two less expensive subs should sound pretty good and will add a nice foundation.

My opinion here.....

If you are going to roll them off that high what is the use of having them? If you want real bass for low dollars look at the older passive Hsu subs that are [as of last night] listed at $350. They produce REAL bass at 20 Hz and are easy to drive. I have a pair, they are not fancy but have good performance. See old reviews in Stereophile and Audio Critic. They may now be on Ebay.