The natural habitat of the coconut palm, for the curious. While it's unlikely that the non-migratory African Swallow would have dropped a coconut in 10th Century England, it's conceivable that the Silk Road could have carried coconuts to Europe.
This is rather a thorny question, given that warhorses did not exist in any appreciable numbers in England until the Norman Conquest of 1066. The English kept horses, but they were strictly riding horses and beasts of burden.
Similarly, I am not aware of any 10th century sources for the price or even availability of coconuts in Europe.
What I can say is that the value of a medieval warhorse could vary tremendously. Defining a warhorse as an animal capable of carrying an armored man into battle, we have low-end rounceys that might cost a few months wages for a laborer to highly specialized destriers equivalent to the yearly rent of a village! This enormous variation tells us something about the so-called knightly class: it was far from homogenous in wealth and status. A poor squire or bachelor could be readily distinguished from a rich lord by the quality of his horse, his arms, and his dress.
