https://www.statista.com/statistics/788557/global-average-se...
And that's the average, likely brought up drastically by the sale of extremely expensive phones. Apple and Samsung's flagships start at $800 and go over double that for their absolute top of the line. Unfortunately I couldn't find the global median selling price of smartphones, but the source above mentions that 58.5% of all smartphones sold during the second quarter of 2019 in Latin America had a price tag of USD$199 or less, and 83% of all smartphones shipped to Africa during the 4th quarter of 2019 had a price tag of $199 or less.
From a quick search, one of the best selling phones right now in India is the Galaxy M13, which is Rs. 9,699, or about USD$118 — barely any more than what Apple charges for a battery replacement in the US (obviously it's not that much for a replacement in India, but it does show how unnecessarily expensive $100 for a battery replacement really is.)
https://www.bajajfinserv.in/insights/best-selling-phones-in-...
In China, those that can afford it seem to buy iPhones (10.7% of sales), but all the rest of the best selling phones seem to be cheaper phones (next best selling is around ~USD$220, and the ones after that seem to be a little above or below that.)
https://www.gizchina.com/2023/03/28/top-10-best-selling-mobi...
In Mexico, 63% of smartphones sold in 2021 were between 3,000 to 10,000 pesos (USD$175 to $585.)
https://expansion.mx/tecnologia/2022/08/04/smartphones-mas-v...
However, if I'm not mistaken that all is for new phones, and most phone sales worldwide aren't new. While used and refurbished smartphones make up only 24.4% of phone sales in North America as of 2020, they make up 75.6% of phone sales in the rest of the world.
https://www.statista.com/statistics/1208609/used-smartphone-...
So the average person worldwide is not buying a new phone at all (and thus spending even less than whatever the median selling smartphone price is, let alone the average.) However, the percentage of phone sales that are used is projected to decrease over time (according to the source above.) Not super surprising, given that while flagship phones have ditched removable backs for a while now, in the past few years more and more budget phones don't even have removable backs, and if you have to spend a significant portion of the cost of a new phone on a battery replacement, then that's a risky decision, as you don't know how long the other parts in the phone will last, and that's a lot of money that you're gambling on it. Sure, 3rd party repair shops in developing countries aren't charging you USD$100 for a battery replacement, but the labor can still easily double the cost of getting a new battery.
At $35 (and that's from iFixit, which if I'm not mistaken doesn't even make the batteries — if the companies sold the batteries directly, it'd be even cheaper), a new battery would be a much smaller risk, and near certainly would lead to less e-waste.