You have most probably browsed through some rent a car company sites, if you ever had to searched for a rental car in Bulgaria with the help of some search engine like Google. You can't help but notice the one digit price tags in the descriptions of the search results like: 9 euro per day for a rental car, only 8 euro rent per day, etc. All these sound great and it's perfectly normal to follow the links and see the offers of the car rentals promising such low prices.
What you'll most probably find out is that the promoted rental car looks more like a scooter than a car in terms of size and trim level. When I say tiny, I mean tiny. Don't expect anything different than a Ford Ka sized hire car. Not to mention that the four wheeled moped is usually manufactured by some "renown" far east brand like KIA. Sadly this is by far not the whole story. If you decide that such korean mini hire car suits your needs, because you are traveling lite - without company and luggage, and don't intend to travel out of town, you still have to meet yet another condition in order to get the bait-price. You have to rent the car for at least a month. Some car rental companies require you to do so for up to at least 6 months.
Lets say one of your million trips meets all the requirements and you are ready to make all the compromises. If you try to make the reservation, you'll most probably end up with a plausible excuse from the car rental guy, saying that the hire car is not available for the period you are interested in. Of course you'll receive some nice offer for "a bit higher" daily price. In fact the super low-cost rental car exists only in the ads the marketing guys came up with to lure more clients to the respective car rental site.