Don't do any online ad as your budget is to small...maybe $500/month wold be fine to start with Google Ads and their shopping ad product. You are better to invest your time in public relations/PR, content marketing and start trying to learn SEO.
If you want to get fast results, I think FB ADS is the solution for your ad. However, if you want to advertise on GOOGLE ADS, it doesn't matter, but I don't recommend it because usually people will be more likely to have a high consumptive attitude when playing social media. Hopefully this can be a reference for you.
Sorry for my bad English.
If your budget is low. I suggest you submit your store content to Google, Bing and other major search engines to generate sales through organic search.
I recommend using SEO APPs such as flare, which regularly and verifiably submit your store content to major Search Engines such as Google and Bing.
Hope this was helpful.
If you have a small budget it is harder, but not impossible. I would try Smart Shopping ads with a smart bidding strategy where you can save some money. Also, I would like to give you a tip to use BlueWinston.com automation tool. They will help you automate your products and campaigns within a few minutes. Also, they can make you pilot campaigns for free.
Have a nice day.