To make it easier to quickly provide reasonable items for purchase to a group of players, consider using the Merchant Tables. Each of these tables has a brief description of how likely it would be for players to encounter such a merchant, along with a list of goods they have for sale. Often the goods either have a range (e.g., d4), or have a percentage chance (e.g., 20%) of appear at all. Notes will specify any additional considerations.
In all cases, assume the merchant charges the amount listed under the Equipment section.