@Mariusz Bojarczuk I wouldn't get entirely discouraged by the recommendations that 30-70k investments are a bad deal. Regardless of the popular opinion, there will always be a market for properties in this price range. Of course, your major turn key companies normally only deal with 3/2 1200 sq ft and up properties in A, B and high C class areas. Although, the fact remains that there will be readily available properties that are 3/1 or 3/1.5 in C class areas that many lower income tenants choose to reside in.
From a wholesaling aspect, I've seen many successful properties sold between 30-45k that were performing well at 650-700/mo and were fully renovated. You run the risk of dealing with a different type of tenant as opposed to one that is paying 900-1200/mo, but the vacancy risks are similar in my opinion. In fact, I'd be almost confident to say that vacancy risks are less with 650-750/mo rent rates as, to me, there is a larger pool of people looking for rentals in this range. In the midwest and my primary market of Memphis especially, there tends to be a range of residents that choose to live a lower income lifestyle and don't mind living in a C class area if the rent is only 700/mo. Excellent property management is your key factor with these types of investments.
If you choose to invest in this price range, I would recommend to do extensive homework on the property, the street, the block and the zip code. Compare the rental rates on the same street and vacancies.
You could also consider working with a local wholesaler or investor friendly agent that can link you to another investor that is unloading their properties or retiring from the business. You can find solid deals in this manner and you can always turn it over to an experienced property management.
Wish you the best in your real estate adventures!