So, had to make this for a project, and thought I would share.
This is a simple PHP script that calculates the BTC<->USD exchange rate on VirWox, after fees.
function getVirWoxRate() {
$curs = json_decode(file_get_contents("http://api.virwox.com/api/json.php?method=getMarketDepth&symbols%5b0%5d=USD/SLL&symbols%5b1%5d=BTC/SLL&buyDepth=1&sellDepth=1&id=1"))->{'result'};
$usd = $curs[0]->{'buy'}[0]->{'price'}; //Price of USD in SLL
$btc = $curs[1]->{'buy'}[0]->{'price'}; //Price of BTC in SLL
$tran1 = $btc-($btc*.029); //Price of BTC in SLL after Fee
$tran2i = $tran1/$usd; //Price of BTC in USD before Fee
$tran2 = $tran2i-($tran2i*.029); //Price of BTC in USD after Fee
return $tran2;
}