A hydro test usually cost about $30.00 depending on where you go. Fire Safe, Maine Oxy, dive shops etc. I usually go to Maine oxy takes about a week I have one Hp tank and a scuba to have done ( scubas are 5 bucks more) I usually find it goood to have two tanks I have a 45/4500 and a 68/4500. Oh I did forget to mention you didn't state whether you had C02 or HP hp tanks are worth re hydroing BUT C02 are not for what it costs to hydro them you can buy a new one. We usually take the old C02 tanks and use them as gong targets for 22lr.