Prices are commonly accepted values for items which are determined by either a set number or supply and demand. RuneScape is an interesting and challenging game, due in no small part to the complexity of its economy.
There are several ways and places in which players can buy, sell and barter goods. Where governed by the game itself, prices will be predictable, or even fixed. At the opposite extreme, when players are directly interacting, the prices will be less predictable, and sometimes even irrational.
Selling prices from high to low
Note that ordering prices in this way intermixes prices in which the player is buying or selling.
The Store Price is the selling price of an item in a store that stocks that item (i.e., the price at which a store sells the item to players). Typically, that is the highest price a player sees for any item. For some items, the appropriate store is the General Store, while in other cases, this price is set in a speciality shop catering to that item type. General store items (for example, buckets) might occasionally show up in a specialist store, but the price and its behaviour will remain the same. Speciality shop items can be sold to a general store as well, but it will sell for a lower price.
The store price is listed in every item's infobox. This price will be at its highest when the store has precisely one item of this kind in stock. The price might drop if the quantity in stock is higher: whether it drops, how quickly it drops, and how many items must be in stock before it drops will depend on the item. Moreover, the store price might well be lower than the street price if the latter is affected by scarcity. It is worth noting that the store price is set within the game itself, and only crudely simulates supply and demand, whereas the street price is set by humans buying and selling (and, indirectly, by bartering) and can fluctuate erratically.
The next highest price will typically be the Street Price. This should vary somewhere between the store price and High Alchemy price if the trading players are acting rationally. The store price should place a ceiling on the street price because a buyer is unlikely to pay a substantially higher street price unless the item is so scarce in stores that the price is irrelevant, such as battlestaves, which have a high demand for Crafting, but Zaff sells only a limited amount per day.
At the same time, a seller capable of the High Alchemy spell has no reason to drop below that price when selling player-to-player — unless, of course, the value of the item is so low that the expenditure of the required runes makes the spell uneconomical. For the same reason, the alchemy prices might not even be relevant and thus provide no floor below the street price. That, in turn, means that players will seldom find the task of finding buyers worth the effort. Thus the curious problem that it is often easier to find a player selling a high value item than a lower value item. Unless you are selling something worthless (examples: bucket or ashes), you are more likely to get a good price on the streets if you use Forums. But, it will generally take longer to sell because sometimes no one wants it. So, sell on the streets if you don't care about waiting or getting a different price every time.
Street prices are only roughly known, since there is no formal exchange in which these trades could be tabulated. The least formal exchanges are those that occur in or near banks or town squares in any world; somewhat more organised are those trades taking place in specially designated worlds, and trades that originate in external forums are the easiest to examine and compare.
Examples of items governed largely by street price include:
High Level Alchemy
The "High Alchemy" price is that of which the appropriate store would purchase the item from the player if the store had none of that item in stock. In other words, the highest price at which the game itself would buy an item from a player. There are, however, exceptions: the specialist shop Grum's Gold Exchange in Port Sarim will buy gold jewellery at a higher price than High Alchemy if none are in stock. The existence of the High Alchemy spell also explains why many mid-range items are seldom traded player-to-player; they are often created in such numbers that searching for buyers would be futile, while the item is valuable enough to make the spell a worthwhile expense.
Low Level Alchemy
The associated "Low Alchemy" spell exchanges the item for the price that would be paid by a General Store, 2/3 of the price that High Alchemy would provide, but this can change depending on the initial value of the item.
In the worst type of scenario — and the only one available to new players and ironmen — is selling items directly to stores. Typically, stores will buy items at half the High Alchemy price. It is also commonly used to dispose of bulk items, which are too cheap to cover the expense of the runes required for High Alchemy.
Grand Exchange Guide Price