I recently put a mobile home on a 1 acre piece of property that already has a mobile home on it. The mobile home that was already here, has been here for about 25 years. There is a 1000 gallon septic tank here. We were told that we need a bigger leach field. How much will this cost ( approximate ) ?

Impossible to tell. We don't know labor rates in your area. Call several septic system installers. Should be able to look at it and give you exact quote based on number and length lines.

In some area installers are now using chopped up rubber tires as aggregate, lowing cost. I had an additional line installed using this and seems to be working fine.

Plus what is the condition of the old field, you may well have to install a new field, how big a field do you need. The county office will have a drawing of all current fields if they were done properly.

We should also ask, who told you this?