Project investment assessments by using capital budgeting techniques are at most in use in big companies, usually founded as Publicly Limited Company (PLC). However, the need of financial calculation of project or venture investment cost-effectiveness in small companies can no longer be considered luxury, but a basic tool for decision making regarding accepting or rejecting of the investment instead. A large number of crashed companies confirm that their business politics seriously lack the basics of economics, starting from planning and business opening effectiveness calculations, to recognizing the moment and making a decision about aborting, or at least changing the business activity in case of bad financial reports. Nowadays practice, supported by small and medium sized enterprises analyses in the region of Europe and America, show that capital budgeting methods are not used enough or at all, while making investment decisions. The most used method is the original period of return, hence not considering the time value of money. The main reasons for this is identified as the fact that small and medium sized companies are significantly different from big, PLC companies, mostly by the capital and management structure, which means they are financed privately by their owner or by money borrowed from family members or friends and have no experts dealing with finances. This paperwork has covered the terms of investments and investment projects, the cost of capital, cash-flows and project selection by use of the scientific literature, and describes the capital budgeting methods in detail. The example described in this paperwork considers the cost effectiveness of opening and running restaurant by a small company, based on three scenarios, by using the conventional capital budgeting methods, and complemented by decision tree as a dynamizing method, regarding all extra circumstances in life time of a project.