Concrete slab vs. crawlspace?

Since my poor old house is non-repairable, we're going to have to build new....looking at a Morton Building shell that we would finish interior.
SO how do we decide on a foundation? We want as inexpensive as possible, but still good as far as energy efficient and ease of future repairs, etc.
The salesman is pushing for a concrete slab, but I've never lived on one and don't know the pros and cons. We are in central Illinois. Any advice or opinions would be MOST appreciated. Thanks!

Alot of areas out your way have such a deep frost that the foundation goes 4 or 5 feet deep. If this were the case your 3 feet away from a basement. Just a thought. If you did go slab on grade, spend the money on radiant floor tubing, easier now than after. Good luck......

Concrete slabs tend to be really cold and uncomfortable during winter. They are common in tropical areas exactly because they keep the house cool during scorching tropical summers.
Therefore, if you go with concrete slabs in IL, you will want a radiant floor.

Crawl spaces are said to be inexpensive but as far as energy efficiency, they are really bad, unless they are encapsulated and conditioned. Studies show that energy losses from vented and dirt crawl spaces can be as high as 35%. Even more (up to 50% more) than that if you have ducts running through your crawl space.

Not to mention moisture problems, mold, mildew and pests. In other words, if you pick a crawl space, have it encapsulated and sealed right away.

A basement, as Triple D suggested, is a bit more expensive to build, but is adds value to your home, and provides additional living or storage space. Spend some money on the best perimeter drainage and waterproofing solutions you can find to avoid problems on the long run.

Thanks for the replies.
We really wanted a basement but cost as well as the fact that there seem to be drainage issues (the corn fields behind us often have six to eight inches of water standing on them for days after a hard rain) are discouraging us from that route.
Any way we go, we like the idea of radiant floor heating.
I guess I just don't understand how everything works on a slab. Are you saying we'd need a really thick slab because of the frost line?
Where do the pipes and ductwork go? (Because we'd still need ductwork for A/C, right?)
If plumbing pipes are buried in concrete, how would you ever get to them for repairs, etc?
Also, if we went with a slab, wouldn't we need to know exactly where all the plumbing goes ahead of time, rather than figure out a specific floor plan later and "do it ourselves"? We really need to be frugal (but wise) at this point because we spent a lot of money for the location. The existing house is "livable" but probably not for longer than 3-5 years unless we put money into it. We were really hoping to get the new shell built and work on it over the next couple of years as time and finances allow, but we don't have a lot of money to sink into it initially.
However, I know that the foundation is the most important decision and what we'd want to put 'smart' money into.
Also, any ball-park figures for costs of various foundations for a 36x48 building?
I'm sure the salesman will have more infor for me, but I don't necessarily trust salesmen. I'd like some non-biased opinions.

Hello DebraAnne:
First, I must say Morton buildings are the most expensive. Second you can get a steel frame building and put it up yourselves for far less money. Third you almost have to build a house inside any of the steel sided buildings.
Yes, you do need to know where your plumbing is going before you start. Some states allow PVC water lines and Drain Waste and Vent lines under the concrete; they just have to be tested before the concrete is placed. Each time any pipe penetrates the slab there should be 3 wraps of corrugated cardboard around them to protect them from the chemicals and abrasions of the concrete.
Your slab can still be 4" thick with the peremiter dug down to the frost line for your area. It also helps to thicken the slab under walls in the house to 6 or 8".
There is a 94% efficient water heater in the Mother Earth News this month which will supply your radiant heat and domestic hot water. I have had dealings with the water heater company, visited their manufacturing plant and sold them. Believe me they really work. You can use PEX tubing for the heat under the slab and you can't imagine how comfy it is. Mother also has several ads for steel buildings you may want to check out.
You may also use PVC and PVC coated pipe for the airconditioning under the floor. Caution; self built means there will be 2 years before you can finish, so be prepared to test your patience.
Glenn