Brighton and Hove Albion. Look at 1997-1999 and what happened to attendances (that were already struggling due to the Seagulls tumbling through the divisions). One of their lowest attendances was barely above 1,000. Once the 86th most supported club of the 92 are now the 14th highest.
european-football-statistics.co.uk
Also, as you mention, spot the years that Coventry spent at Sixfields and St Andrews (albeit the latter did cover the COVID-impacted attendances too). It's not tricky.
european-football-statistics.co.uk
Both of those clubs have historically larger attendances than us. Bigger places and bigger clubs, after all. A groundshare would maybe see 1000 season ticket holders go along to every game and then maybe another 1000 at most occasional fans. 3000 regulars would be wildly optimistic.
Hold your nose and pay Kassam versus a ground share any day of the week, if that option is available.