You are coming on business
Whatever kind of business you have in St Petersburg it is very helpful to use an assistent who could act as your guide, interpriter and driver; three in one. You are going to be mobile, comfortable and on time to all the appointments with your personal interpriter.
In case you have some free time (even a few hours) it is a good chance to combine your business with a pleasure of seeing the best sights of St Petersburg without any special arrangements.
I charge $US 25 per hour for the package, which includes guide services, interpreting and transportation by my car.