Q:

Would upgrading my basement with sandstone blocks be worthwhile?

Having a look at an old farmhouse that is for sale in the area, and as with most houses in the area of this age the foundation is built on red sandstone blocks, around five feet deep, with a dirt floor. Not very useful to have for much of anything outside of storage space, but it has a lot of floor space as it has the same square footage as the other two floors (roughly 1500+ sq ft)
What I'm wondering is if it possible, and if so, worthwhile to upgrade the foundation to the following:

Be at least 7 feet with concrete/finished floor
Able to keep the sandstone walls, if possible (mainly for aesthetics and hence resale...I realize concrete is stronger and probably better insulated)
Reduce the amount of poles that are in the basement (there seem to be a few of them that dont' have much of a logical layout to them.

Any advice would be most welcomed.
EDIT: Here's a picture of the enterence to the basement in question. I sadly didn't get any pictures of the basement due to the limitation of the camera that I have. You can see the floor is still the dirt floors, with the original stone steps and sandstone blocks. Those blocks are what they used for the foundations, with roughly 6inch diameter wood pillars within the floor area.

A:

You have a couple things going on here:
1) The posts.   an engineer would have to evaluate to be sure, but it's most likely that you will not be able to remove the posts without providing beams of some sort to span the space between the walls.     Their irregular arrangement probably lines up with walls that they are supporting in the first story, which in turn are supporting the floor of the second story.
2) Clearance.   Digging deeper to get additional clearance will be challenging, because you will have to leave the footers under the existing foundation in place, and not undermine them.   This means you will likely end up with a floor that is a fair amount smaller than the existing space.    Also, you will have to support the part of the house that are held up by the posts while they are being relocated/lengthened.
In either case, you will need advice from someone knowledgeable in building structure and foundations.
Overall, it may be easier/cheaper to raise the level of the house and add additional height to the existing foundation (if it is in good enough shape to take the additional load) than to dig deeper.   A contractor that is experienced in this will know how to support the house while it is being raised, and you may be able to include new support beams to eliminate some or all of the posts at the same time.

A:

When I drive through places that have a lot of old homes with dirt-floor basements, I also see a lot of billboards for house lifters, crawlspace conversions etc. Some are fullsized billboards and some are just small plastic signs nailed to hydro poles. Call one of those places and ask roughly what to expect per square foot. Sure, it will depend on the house blah blah but they can tell you whether it's closer to 5K or 50K. Just seeing how many such business are advertising in the area will let you know what kind of choices you are likely to have. And if it's a small enough community, the person may know some details about the house and be able to give you a more accurate estimate. 
I think (based on the fact that people do it) it's cheaper to dig out a basement than to add that square footage onto the house any other way. So that should give you an upper bound, anyway.

A:

This is definitely doable, but I would definitely question if it's worthwhile.  It's expensive, and depending on the condition of the rest of the house and the area, it may not add the amount of value to the house that it costs to do. Of course, if it's valuable enough to you, and you're not planning on selling soon, you may not care, but this is definitely a consideration, especially if you're borrowing money to pay for the work.
It most certainly is not (entirely) a DIY job. You need at the least a structural engineer to evaluate posts and supports. If you dig down, you'll need to replace the existing posts - likely with modern jack posts. If you want to remove some of the posts, then you'll need to run new beams to support the area, which again requires a structural engineer to properly evaluate. 
If you're going to dig down near existing foundation, you'll probably also need to extend the footings downwards (there are a few techniques for doing this). 
Are you going to be able to dig down? How deep is the bedrock below the house? How deep is the water table (are you going to just have endless flooding issues)?
You can also jack the house up, and pour a new foundation (raising the height of the house), but this may not meet your criteria of reusing the existing sandstone, and has many of the same structural/support problems. 
If you hire someone in, be sure that you check the references on them and see some other work they did, and that they're insured, etc. This is the sort of job where if they mess up, your entire house can be irreparably damaged (think, crack going through all floors up through a load-bearing wall).
The other thing to consider is the condition of the house itself - can it hold up to this kind of a reno? You're going to have temporary supports in place, and you're going to be shifting around the weight loads from the house. The floors and walls WILL move a bit, and may cause damage as a result. If the house is in poor shape, you may end up spending a ton of money/time fixing all sorts of other cracks, jammed doors, broken tiles/hardwood, etc.

