Suffice it to say, that it must be understandable that his true first editions of his An American Dictionary of the English Language (1828, printed by S. Converse) could be worth tens of thousands of US dollars. Luckily for the collector however, this book was so successful that there have been many printings in Webster's own lifetime, and many of these are still affordable and valuable to this very day.
Consider instead perhaps, the 1848 edition of An American Dictionary of the English Language, printed by George and Charles Merriam of Springfield (and forming the basic working partnership that became the Merriam-Webster that we all so love and enjoy today). A first edition in good condition can still be found for as little as a thousand dollars - which would be a remarkable asset to any collection!
Given Webster's interest in pedagogy, there are still many very fine textbooks which are available in their true first edition form which would also make a wonderful edition to any antiquarian collection. Webster's A Compendious Dictionary of the English Language (1806, Sidney's Press for Hudsom and Goodwin and Increase Cooke, Hartford and New Haven) can be found for much less than a thousand dollars if you are willing to search around for it.
A fine example of Noah Webster's legacy might also be the Dictionary for Primary Schools (1838) which would vary in price from the very affordable few hundred dollars to almost one thousand, depending on the quality of the edition. As a children's textbook, many of these original first editions have suffered from wear and tear, and the not-so gentle ministrations of their primary school owners. Whilst these marks and marginalia would bring down the price of any collected work, to me it only makes them the more valuable as a piece of historical record!
Webster, Noah. A Brief History of Epidemic and Pestilential Diseases. Hudson and Goodwin: Hartford (1799). 2 volumes; Signed Edition; Full title-A Brief History of Epidemic and Pestilential Diseases; with the Principal Phenomena of the Physical World, which Precede and Accompany Them, and Observations deduced from the Facts Stated
Webster, Noah. A Dictionary of the English Language. Sidney's Press: New Haven (1807). Full title-A Dictionary of the English Language; Compiled for the Use of Common Schools in the United States
Webster, Noah. History of the United States. Durrie and Peck: New Haven, CT (1832). Full title-History of the United States to Which is prefixed A Brief Historical Account of Our [English] Ancestors, form the Dispersion at Babel, to Their Migration to America and of the Conquest of South America by the Spaniards
Webster, Noah. An American Dictionary of the English Language. Harper and Brothers: New York (1846). Revised edition
Webster, Noah. An American Dictionary of the English Language. George and Charles Merriam: Springfield, MA (1848). 2 volumes; Revised and enlarged by Chauncey A. Goodrich; First Merriam Edition of Webster's Dictionary
Webster, Noah. An American Dictionary of the English Language. George and Charles Merriam: Springfield, MA (1849). Second edition of the Merriam-Webster Dictionary; Revised and enlarged by Chauncey A. Goodrich
Webster, Noah. An American Dictionary of the English Language. George and Charles Merriam: Springfield, MA (1860). 2 volumes; Revised and enlarged by Chauncey A, Goodrich
Webster, Noah. An American Dictionary of the English Language. George and Charles Merriam: Springfield, MA (1864). 3 volumes; Revised and enlarged by Chauncey A. Goodrich and Noah Porter
Webster, Noah. An American Dictionary of the English Language. Johnson Reprint Corporation: New York and London (1970). Limited Edition; 500 copies; 2 volumes; Introduction by Mario Pei