What is the approximate cost to store a mapping to be used in a contract?

Question

Given a simple address to address mapping as follows:

mapping (address => address) public matches;

Can someone give me an idea of the cost in ether to store something like this in a solidity contract? I understand that there are gas costs associated with every alteration of the blockchain and storage is expensive but I am having trouble finding estimations of what simple storage like a mapping would cost.

The feasibility of my Dapp idea depends on storing mappings from address to address cheaply. Ideally around 1 cent USD or so. If mappings are more expensive are there any workarounds? Thanks.

Answer 1

In the simplest implementation I can think of:

pragma solidity ^0.4.6;

contract Mapping {
    mapping(address => address) public matches;

    function writeMapping(address addr) {
        matches[addr] = msg.sender;
    }
}

1. First write 42K gas
2. Overwrite 27K gas

Gas price in Eth and ETH price in $ both float on markets, so any estimate would be a forecast.

The gas cost operations are knowable and should be consistent (in the example) but are subject to periodic change at the protocol level. That is, if the cost/OP table is adjusted in the future.

Hope it helps.