If you are buying things purely based on the fact that it's the lowest price, there are one of two things that are happening:
1. The company selling the product at a lower cost has reached economies of scale and can afford to sell you the product at a cheaper cost than other competitors
2. (This is much more likely than the first scenario) You are buying a sub-par product, whether tangible in the product itself, or in the followup support/service related to that item.
What most people don't think about when purchasing a product is the aftermath of that decision.
Let's say you are in the market to get some web hosting. You have tons of options, but two stand out. The first is a cheap $6 a month package, and the second is a little pricier at $30 a month.
You decide to buy super cheap web hosting at around six bucks a month.
The product is 'okay' (until you outgrow it), and it does what it claims it will do for 6 dollars a month.
Great! Now let's say a year later, you run into an issue with said hosting product, and it needs to be fixed. The fact that the product is so cheap to begin with means that service is limited and spread thin across their hoards of other cheapskate buyers.
You end up having to send a bunch of your own time fixing things. Hours and hours of your precious time, valued at X dollars an hour.
I charge $125 dollars an hour for my time.
This means spending 6 hours fixing a problem is (in terms of opportunity cost) costing me $750 dollars.
Now that other "expensive" option that was pushed aside for the "cheap/easy" hosting solution looks like bullshit compared to the 30$ a month option that runs automated backups for you and has customer support that will run through the trenches for you.
It would have cost me $720 (30 x 12 x 12) for two years of hosting from the more expensive 30$ a month hosting option, where I wouldn't have to fix my own problems (or never run into them in the first place because of better site security).
Beware of hidden "what if" costs.
You get what you pay for.