Less than $100 ~ £75 so far, but I've only just started.
The tank, filter and heater were free, borrowed from my sisters old stuff.
Since then though, i've spent around the £75 mark on accessories and other misc items, but once bought are there for a good long time. Id say the most expensive item has been the master test kit at £17. everything else has been 5 quid or less.
Oddly i look forward to the day i've spent hundreds/thousands, hopefully I'll have a good reward to show for it.