On a Colchester United site, they list the lowest crowds to watch Colchester ever. It includes 710 that saw Merthyr v Colchester in December 1990. Merthyr finished 9th that season.
https://www.coludata.co.uk/content.php?pg=sipg&pd=1140
Same season, they had 1,175 against Barnet - Gary Bull scored a pen for Barnet.
1989/90 they had 2,003 against Barnet, would have been one of their first home games at that level.