That's definitely an interesting question @sudipmus. If I have $100 to invest for my blog, then I'll probably:
1. Invest $1 for buying .com GoDaddy domain name.
2. Invest for a good branded logo!
3. Will wait for Black Friday or Cyber Monday, then grab a good web hosting deal!
4. Invest for G Suite email address (like firstname.lastname@example.org).
5. Grab some premium plugins like WP Rocket, Yoast SEO Premium, etc.
I hope by now $100 should be over, but these will be my top spendings! I won't exactly invest for Facebook Ads at this point, but I might do that if I get some extra bucks in future. :') What about you?