I only ever used two :) One other one which got used occasionally, bought it for a christening as it was a dressy one.
Stretchy wrap, home made, £15 for two (one for the wash, but totally unnecessary, ended up giving to a friend who never returned it)
Toddler Patapum, £45, used for front and then back carries once baby grew out of wrap sling.
Ring sling, £30, made of silk for Christening/weddings, used occasionally round house but never really got into.
So total = £90 (£60 essential)
I spent £220 on the first pushchair we bought and then £70 on an umbrella fold, and £40 on a different umbrella fold after I split up with XP and he took the first one for access visits.
IME they end up costing more because people get addicted to them
and "need" to have more. You don't actually need more than two. You can get away with one if you use a woven wrap from birth, but they're for hardcore babywearers!
I'd recommend a stretchy wrap for babies and a structured carrier of some kind for 9 months + if you want to keep costs and complications down. A one shoulder one is handy for the pick up/put down constantly stage, and they're pretty cheap, if you want an extra one.