Hi Liz. Yes, not only could be costly, but it could also be impossible depending on the soil. You really need a whole lot more information about this septic system. If your septic system fails, the property becomes uninhabitable. There are so many variables to septic systems that no one answer can cover it all. I suspect that there may be a problem with the leach fields. There are quite a few new septic systems on the market these days, but they can be costly ($5,000 - $25,000 or more) and not all of the new system have been approved in all areas. If the price is right and you know that you'll be able to remedy the situation, it may be worth it. Good luck.