You ask, " I own a 1963 mobile home on 5.5 acres of land in Deering, New Hampshire . I am in need of a new leach field. How do I find out the blue book value of the house and land?"
This is really a three part question. But it seems to me you are asking what you could sell the home for, and how much would a leach field cost--so you could factor in the expense of that repair--to determine what you would net.
Generally speaking, mobile homes older than 20 years are hard to finance. And single wide units over 20 years are almost impossible--so have almost no value. The land may have some value, and the home will probably sell for the value of the land. A new septic field will cost somewhere between $5,000 and $15,000. But if the home is selling for the land value, then you can forget the cost to replace the field.
Land may require a 50% downpayment, so that may also be a tough sale just now.
If you choose to go with a new field,I think the best value is a Presby System--check them out in Google, you should budget $7,500 or so for that system.
To get a hard dollar figure, call a Realtor in your area and ask for a CMA (Comparitive Market Analysis), don't bother looking at your property tax bill, it'll be off by 25% at least.