i need 20 meter speaker wire, decent quality

With runs of this length, I would steer away from multi-stranded cables with heavy coatings. Look into some of the solid-core high purity copper cables on Audiogon for $10/ft. They are well suited for long runs and high-current amps like yours, they're reasonably priced, and sound great when properly broken-in.

You will probably need just one per speaker if they only go across 6 feet of carpet once coming out of the wall.

Merrill;
I would not recommend using the standard 12 or 14 gauge solid core "house wire" as Morrow suggested as a speaker wire. It has heavy insulation all around, and sonically it is rather harsh and edgy. I have experimented with it for both AC cords and D.I.Y speaker cables with poor results. I tried the Anti-Cable solid core wires a few years ago, and was very impressed by some things it did in two different systems I had, but found it had tonality issues which I could not live with. I later tried a similar solid core cable (but cryo-treated) by JW Audio. It had none of the tonality issues that bothered me with the Anti-cables, and the detail and clarity was the best I have heard in my system at this point. My previous 6 foot pair of wires retailed at over $1,200, and I quickly sold them for half that amount. I was quite shocked that a $60 pair of cables could sound so much better in comparison. They do offer a 30 day trial, but you might want to see if they will still do so on such an unusual length. At $10 a foot, you will only be looking at a bit over $600 for a pair. That would be far more reasonable than a high quality set of 60+ foot interconnects!

I did not know you were were looking to bi-wire. I would guess, in that case, you would have to double the price for twice as much wire. I would not think that they would have to charge quite so much extra $ for 4 more spades on the speaker ends. I could understand a few extra dollars, but not four or five hundred dollars. If you have carpet on the floors where you are running them, it would be a good idea to raise the wires off the carpet a few inches to avoid any static interactions. A simple solution is to purchase some (in your case... MANY) inexpensive, round, 3 foot wooden dowel rods and cut them in half to make some simple "tripods" to keep them of the carpet. Home Depot sells approx. 3/8" diameter ones for very little money. You can even stain or gloss them to make them more attractive.

You might check with your installer to see if it would be easier for them to run 2 separate runs of the solid core cable through the walls at a time if you were thinking of having the cables bi-wired on the amp end. The solid core wires are fairly stiff, and trying to push or pull all four cables from a bi-wired pair through the wall at the same time may be a bit tricky for them. They will go through easier in most situations one pair at a time. You would then just attach both spade ends (2) to each output binding post of your amps for the two pairs, instead of crimping/soldering the wires into a single spade at the amp end. This "double run" would be the same sonically, but possibly easier to handle around tight bends in the walls if that might be the case.
I just noticed that you showed two different stereo amps. Are you bi-amping the speakers with the two amps, or just using one of the amps and bi-wiring it to the speakers?