I'm wanting to build and would like to do ICF but the cost is so high that I can't afford it unless I cut somewhere.  I'm considering doing a conventional 9' basement, 10" thick with a 9' tall 6" thick icf on top of it.  I have a cost quote of around $5.00 to $6.00 per foot for the conventional basement with footing.   My questions are:
1.  Would rigid insulation work fine on the outside of the basement wall?  I've  found some 2" thick for under $1.00 a foot.  Later , perhaps years, I could do the inside walls.  But for now it would keep my cost low. 
2.  I know there are different types of sheet insulation.  Some with reflective metal on them.  What different types should I look at?  Which would be the best?
3.  What should I use to seal the conventional poured basement with that I could attach the ridgid insulation to and it not react with it?
4.  What  is the best way to attach the rigid insulation?  Should I seal on the outside of it as well?
5.  I was thinking of putting a metal termite shield between the icf wall and the conventional basement with a small gap of no insulation at all on the conventional basement so I could see any possible termite trails.  How else could I do this so I could still see if I have a termite problem and insulate or would a foot gap with no insulation be that big of a deal?
 

I am no expert but I have been doing a lot of research on this subject and I'll give you the OPINIONS I have formed.

1. Yes rigid foam insulation will work fine on outside basement walls. It is important to break ground contact with the walls when possible.

2.  Reflective material (radiant barrier) is near worthless under ground.

3. Since cost is an issue, coat your exterior basement wall with a damp proofing product then wrap them in a poylethelene sheet product made for that purpose in accordance with the manufactures instructions, then install the rigid insulation. 

Foam will not react with concrete anyway.  The rigid insulation will also keep rocks in the back fill from damaging the damp proof.

4. The attach the rigid insulation with an adhesive.  Where can it go after the wall is back filled?  Above grade you can use concrete anchors.  

5. Drop that idea.  Your well sealed concrete walls are good enough.  Just keep the area around your house clear of wood and vegetation that provide food and moisture.  Don't have any wood lying around. You can also apply termiticide to the graded soil as the home is being built. 

A better idea to your method is to set bait stations in the ground every ten feet or so around the perimeter of the home. Untreated wood is installed in the bait units to determine if termites are active around the house. The units are checked once a week, and if live termites are found, the wood is replaced with a toxic bait that is ingested by the termites and carried back to the colony.  MOST IMPORTANT, keep the soil around the home DRY, termites need water, see below

6.  The most important thing about basement walls is keeping water away from them.  Think drainage, drainage, drainage. 

You must move downspout water away from the home.  You must slope the grade away from the home, 4 degrees is minimum.  You must install a proper drainage system for your soil conditions around the foundation and walls.  That is where to put your time and money.

DRY earth is a fine insulator.  Consider wing insulation.  That is installing layers insulating material and water barrier below grade horizontally from the basement wall, sloping away from the walls. 

(Do not insulate the interior walls for several months after they are poured so they can dry out first.)

Another added measure that we use commonly is what they call air-gap membrane. It is also called a drainage plane or dimple sheet. The idea is that it acts as a decent membrane, but more importantly it creates a nice 3/4" air space behind that acts as a drainage plane for any moisture. This drainage plane minimizes the hydrostatic pressure against the concrete wall and is fairly inexpensive additional water mitigation that creates a more redundant system. The 2 companies that I know of are Cosella Dorken (their product is Delta MS) and Armtec (their product is platon).