Interconnect Cable Length

Quick question - I have a preamp with 75 ohm output impedance and an amp with 47K ohm input impedance. What would be the maximum length of interconnects I could use between them without sacrificing sound quality? I know the answer will depend on the quality of the interconnects but I'm trying to work within a $200 budget, if at all possible. For example, I see the AudioQuest  Evergreen cables sell for ~$120 for a 12 meter length. Also, is there a general rule of thumb for trade off between speaker cable length and interconnect length, assuming comparable quality cables?

Thanks in advance. 

Twelve meters is a bit long for line level in unbalanced interconnects; there will some signal loss.  Any chance you have a balanced option on your preamp to amp? Otherwise, in general and in my experience, it is better to keep unbalanced IC length short and go with length in the speaker cables.  Obviously, you likely have spacial requirements not fully explained here so my comments are conditional.
Thank you. Unfortunately I don't have balanced input/output on either of my devices and they are currently 1.5 meters apart. My spacial limitations are based on the fact that I'm currently using my in-wall speaker wiring - 12 gauge, and each run is roughly 25' from the amp. I can forego the current wiring and move the amp closer to the speakers by using ~15'-20' interconnects. Realistically, I don't need 12 meters cable, more like 7 meters. Just as an aside, I had mentioned this in another thread that I'm seriously considering purchasing a pair of Cary SLM-100 monoblocks from a friend and I was warned against running 25' speaker wires with those amps. They do have much higher input impedance - 150K ohms, so that might help with the interconnect length. Ideally, I should move the entire audio system including all the sources to the opposite side of the room near the speakers but that would require significant redecoration and technically not an option, not at this time anyway.
Just a quick update and another question. Since my last post I read up some more about the Carys and their very high output impedance and decided to go with a solid state amp and bought a perfect condition, recently serviced McIntosh MC2200 stereo amp. It sounds beautiful. Here is my related interconnect question:  assuming very high quality cables, do you guys think there will be noticeable difference between a 3 meter and a 6 meter interconnect lengths? As a reminder, the preamp output impedance is 75 ohms and the MC2200 has a 100K input impedance. Thanks again.
 For years  I used a 7m IC between my amp and pre amp. I always obsessed with how  degrading this must have been, but I had no options. When I finally was able to re arrange my system and went to a shorter IC I can honestly say I heard absolutely no difference. Dont drive yourself crazy!
With 47K input impedance, there should be no problem.
Your total active resistance will still be within tolerable single digits of ohm if not less.
Going silver is far more pricey, but active resistance nearly halves vs. copper.

Thank you guys for your input. The 6 meter cable is an Onix Master series that retails for $1800. I bought it for quite a bit less along with the MC2200 amp. I did an A and B test comparing it with my 3 meter Pangea cable (paid $150) and could not tell a difference. I have it all now hooked up with my preamp driving two separate amps and pairs of speakers in two adjacent rooms. I must say the Onix cables were probably built for professional use since they are about 5/8" thick with an almost indestructible shielding. Completely overkill.
I'm sure you're not the first heard by me who didn't feel any difference between hi-end and low-end cable or longer vs. shorter one.