The value of different kinds of meteorite
Mineral fragments falling from space can range from moderately to extremely valuable: anywhere from 5 per gram to truly astronomical figures.
The basic value comes from the natural interest in holding something literally out of this world. Other than that the value depends on any story associated with it, and sometimes the exact origin.
The famous Barwell meteorite, which fell on Barwell, Leicestershire on Christmas Eve, 1965 now sells at around 200 per 3g fragment. The total size of the meteorite when all the fragments had been collected together was 'about the size of a Christmas turkey' - the comparison probably due to the season.
A much larger meteorite - 56lb - hit Wold Cottage in East Yorkshire over 200 years ago in 1795. Fragments of this in particular have increased in value sharply, with tiny pieces worth 100 a decade ago now worth 240.
The composition of meteorites is important to their value. Iron rich examples such as pallasites are rare and can be worth more.
Of special interest however are achondrites. These are rocky meteorites, but ones which do not contain chondrules - round grains. Achondrites are taken to be the results of impacts on other heavenly bodies and did not form in the same way.
A Eucrite (type of achondrite)
That is, achondrites may originate from the moon or even Mars. These rarely reach Earth, but a few do. As these are the only sources of material from another planet, they have sold for tens, even hundreds, of thousands of pounds per gram.
Needless to say, no one should consider buying a supposed Mars or moon rock without having it analysed first. No one wants to end up like the Rijksmuseum in the Netherlands.