There are some very good articles, info, how to’s and videos on the REL website.
This explains the 3 common ways to connect a Sub:
Your budget will get a used REL T5i T5x T7i T7x with a bit of patience (white ones are usually cheaper) or one of the SVS 1000 Pro, possibly a 2000 but that’s an older design so I’d stick to the 1000 Pro or one of the equivalent BK 400 series.
Check out Richer, 7Oaks and Peter Tyson both on their sites and eBay.
The T-Zero didn’t do much in my smallish home office, barely noticed it, a T5i was a real improvement and imho well worth the extra £. Later on I picked up an original T7 for £150, cosmetically challenged but sonics are 100%, ended up buying another T5i and using them stacked in Mrs AA‘s system - MA GR20.
Well worth a look on forum classifieds if a used bargain appeals, Mavs, AoS and PFM and putting in a WTD Ad.