Beyond the other good recommendations here, go on amazon and do your search for "mechanical keyboard" armed with a bit of information first, like knowing that you won't find a good mechanical keyboard for under $40.
Then click on one you're interested in that has at least 50 reviews and check that it's been for sale for at least 6 months. If anything hasn't been for sale very long, or hasn't gotten many reviews, it's likely a poor product.
Now for the other important bit. Go to the reviews and sort them by NEWEST. Every scam product in existence gets the initial ball rolling with fake/paid reviews, but then stops after a couple months. So when you sort by newest and look at the most recent 20 reviews, those are almost always mostly real people. Those are what you want to look at. If a product is rated 4.5 stars with 500 reviews, but the most recent 20 don't average out anywhere close to 4.5, you know the product is a lie.