There are only two very rare stamps which reach the stratosphere of price when sold at auction. The remainder of the material is mostly within budget of most philatelists, even those wishing to build a specialized country collection of Liberia. Even the prices for the first issues are reasonable.

The number of varieties are incredible: numerous examples of perforation, color, error and overprint varieties exist as well as pre production, items such as essays, proofs, and trials all of which are, for the most part, available.

The latest, and only, "complete" Liberia specialized catalogue was published by Lothar von Saleski in 1975. In spite of his enormous effort, it remains incomplete and sometimes inaccurate. 
Philip Cockrill, one of the best experts in Liberian philately, has written many studies about surcharges, plating, cancellations, postal history and forgeries which supplement the catalog. These works are not, to my knowledge, currently available on the internet. This online catalog of Liberia (1860-1960) will mainly rely on Philip Cockrill's works.

Postal history is the aspect of Liberian philately that has the most work yet to be done. Early internal covers, specially from 19th century, are rare because the people were mostly illiterate. Most letters sent to foreign countries were written by missionaries or the extreme upper class.

This catalogue does not have price listing because the market is always fluctuating according to the supply and the demand. Most of the varieties are not even listed in priced catalogues and this is not the goal of this site. But I'll always try to grade items as  scarce, very scarce, rare or very rare as a relative indication of their value. "Common" or "less common"  should be referring to stamps under $200 and would not be mentioned as is in here. For Liberia, common relates to a cash value under $200.