You can always run cable or conduit on the surface but really, an electrician with a clue can cut minimal holes (which can be patched) to fish the feeder cable through to the new subpanel.

If you really need 100A, you have to known what type of cable you are running. THHN (individual conductors in conduit) or USE cable will support 100 on 3g. If you are going to use NM, you'l have to go to 2g.

Of course, how did you arrive at 100A? It's unlikely you need anywhere NEAR that amount. 60A would be plenty fine and can be done with 6g.

Unfortunately, the way the floor joists run under the house necessitates boring holes through in order to get to the basement. There is no way to fish wire/cable through without doing some demo work.

I really don't need a 100A panel, but the prices I found (quickly at the big box stores) were comparable between 100A and smaller boxes. In reality I could get away with 50-60A. I suppose I could make my life easier and just run a 60A breaker in the main panel and use the 100A sub panel with #6.

That still leaves the question of actually routing the wire since I would really rather not tear apart the garage.

You need to hire a competent electrician or develop the proper skills yourself. You do not have to demolish the garage to run wiring through the garage even if you have to run perpendicular to solid wood floor joists.

I had no intention of demolishing my garage. As far as I can see, there is no way to accomplish what I want to do without cutting out a 6" width of sheetrock across the width of the garage to get a right angle in to drill holes. As I said before, I would prefer not to do this. I didn't think they had invented 14' long drill bits that require zero clearance yet.

If you have any suggestions i'm all ears. Also, as far as developing the proper skills, that's why I asked in the first place.

Not 14' but certainly 3'. You don't need to cut a trench across the ceiling. A few small holes that can easily be patched is all that is needed.

Personally, I'd go with the conduit. If you use THHN, the ground doesn't have to be as big as the hot/neutral wires.

I spoke with the licensed electrician at work this morning regarding my options. He recommended two ways of doing it.

1. Run SCH80 conduit as you recommended from inside the basement across the ceiling to the wall above the panel. Use a sweeping 90 to enter the sheetrock of the wall and down to the panel. Use individual THHN conductors. I need clarification if I can use a single color and mark the terminations with appropriately colored tape. It will still require some patch work on the wall, but much less than patching 10 holes in the ceiling from drilling joists.

2. Use SER cable and exit the sheetrock at the ceiling above the panel. Run the cable across the ceiling and attach with SER staples/clips and go through the sheetrock/joist into the basement.

3. I guess I could still use conduit and still run all my new feeds back to the panel, but that limits expandability later. I also don't know exactly what I want to run yet.

Be advised that adding additional conductors later to a conduit that is already partially filled is extremely difficult, especially if elbows are involved. And multiple elbows compounds the difficulty. So whether cable or conduit, the initial installation should be considered to be the final installation.

bus driver, precisely why I would prefer to opt for a sub panel and not just individual circuits run to the main panel. My main service is 200A and I am not using even half of the available slots. Putting a 100A sub panel is way overkill, but it leads to flexibility later. The unfinished basement will be cake to wire once the sub panel is in.

I think opting for THHN wire running in conduit is probably the better choice long term. 60A vs 100A would probably be determined on cost of the wire. #3 for 100A would cost roughly $180 vs $100 for #6, so roughly double the price.