Best cable for a long, long run?

I need help choosing cables to make some long runs from our amp to our speakers. We also need long cables from the amp to the preamp. The run from our 'built-in' stereo cabinet to our new speakers is about forty feet. I'd like to make this run under the floor, running the cable through the ceiling of our finished basement. I also want to relocate the amplifier to the basement, just under the cabinet, and make the speaker cable run from there. This means an 8' - 10' run from the Levinson 380S preamp in the cabinet to the Levinson amplifier in the basement and then the 40' run from the amp to the speakers, which are Revel Gems. I'd like to use quality cable to make these runs, but with these lengths it could get pretty expensive! Is there a 'price-range' I should be looking at to insure that I'm buying something suitable? I really don't know much about cables and would appreciate any suggestions or advice you might have on how much I should spend, type of cable, brands, etc. Thanks for the help! Kurt
You mentioned "quality cable". You also imply "flexible" cable. On those two alone, the Nordost line of cables would be fine. But then you said "inexpensive" cable. My advice would be to pick up a great deal of long runs off the used market - look at "FATWYRE" the cable company for extensive selection. You may not be able to afford 40 feet of Nordost SPM or Red Dawn. Ofcourse, you may be Bill Gates and I don't know it.
if you haven't made a purchase yet, you should consider moving the amp even closer to the speakers (underneath them?) and using a longer, balanced interconnect between preamp and amp, with shorter speaker wires. That's what I did for my thirty foot run, and it made a HUGE difference.
I would try DH Labs Silver Sonics T-14, This cable is about $4.00 a foot, and it makes an immediate difference in the sound, that you can actually hear! It will make your system sound so much better you wont believe it. I see people getting rid of there super expensive cables(some as much as $1000 or more) to buy this stuff at a local dealer. Best I ever tried.
Thanks to everyone for the advice. Aragonace, I'm going to try to move the amp underneath the speakers and use balanced interconnects as you suggest. All I need now is an amp with balanced inputs! But that might actually be cheaper than 40 feet of some of this cable. If I can't move the amp, then something in the $4.00 per ft range sounds like a good option -- thanks 'Rmal'.
Best cable for very long runs, for most systems, would be Cardas Neutral Reference. It was designed with this in mind (very long runs).
Purist Audio Design.....Purely the best in THE LONG RUN! Visit them at their Website. Jim Aud is an Audio God!
I'm using balanced interconnects through a unbalanced amp. HOW?? Simple. I bought a pair of Neutrik connectors that convert balanced into unbalanced. As for my single-ended preamp, I used connectors that convert RCA to balanced. So before you choose to spend some $$$$$$$,(maybe a lot more)give it a try. It'll save you alot of $$$$$$$.