There is an extensive thread if you do a search about the cost of the various waste treatment systems.
You almost certainly must apply for planning permission for your new septic tank and without doubt you must apply for permission if you want to install it in a new location. Your looking at spending 5 or 6 k for that at least with planning, testing, purchase, installation.
1/3 of an acre would not be enough to build on (if your were thinking of selling it as a site) in a rural area but may get permission in an urban setting where connnection to public sewer was available.
If your not thinking of it being used as a building site there is not much use for a 1/3 acre or nothing I can think anyone would pay very much for.