You def don't need to spend to have an effective home gym but here is what is in mine...

Treadmill ($2,000 4 years ago)
Boxing bag and stand ($300 approx)
Weighted boxing gloves ($50)
Boxing inners ($15)
Weight set with barbell and dwell capacity ($50). I dislike this though as very fiddly and I like to be quick with little rest time.
Fit ball ($20 years ago)
Resistance bands (set of 3 $30). These are awesome, you can do bucket loads with just these!
Weighted skipping rope ($15)
Spikey massage ball ($20)
Yoga Matt (Christmas pressie)
Trx band ($110). Love this
Boxing focus pads nuts ant remember cost
I think that's it. I have a few pilates balls as well. I have built mine up over the last 4 years. I still want to get a few things. My most used equip is my treadmill, fit ball, Matt, resistance bands, trx bands. I haven't boxed much since I locked a facet joint in my neck and shoulder.