$150 for SEO or Banner ads?

I have got a small budget for promotion of my new site that established since 3 weeks ago but traffic is still very low. I was wondering if it's better to spend $150 for a SEO expert to improve my site's SEO or better to buy some banner advertising for 3 months for $150?

The 3 month ad will be over in 3 months, but might generate more traffic to your site.
The SEO work will have lasting effects on your site.

$150 is a drop in the bucket for SEO work though, you probably won't see any immediate return on your $150, but it will get you started down the right path

Both those options are too risky for a new website and might not bring a good ROI (return on investment).

People these days use Ad Block addons on their browsers so only a few people will see your ads. Some website themes/templates don't even show banners on mobile. Banner ads have a lot of disadvantages these days and I would never recommend them to anyone.

I have a website that gets a lot of traffic but the banner ads clicks are just crap, I'm even thinking of removing them.

If you choose to do SEO, then it will take some time to start seeing some good traffic with $150 unless you rent some good backlinks for about $15 each or even less (which is also risky). If you decide to build a PBN you might get 3 or 4 websites, which might not be enough depending on your niche and competition.

With $150 I would do Facebook Ads or Bing Ads. This way I will spend less and still get lots of dead cheap traffic and most importantly, lower the risk. But if you insist on doing banner ads then do them via Adwords, they're a lot cheaper that way and you'll be paying per click instead of impression.