Check lot size as new state regs I believe require 2 acre min lot size. most older systems were put in under less strict standards. If you need to remove system and replace where current is, the removed material is treated as hazardous waste which is expensive to deal with. TYpical life for these systems are about 30 years but depend upon how used and maintaned. If city sewer is available for similar price home with other equal features I would opt for sewer. Usually though septic served lots are larger (that is the trade off) new systems could run under 20K for conventional system (for 4 bed home) to twice that depending (raised bed for example). If it has a well that is another story.