Rick talks sense. Don't forget, there is still a million dollars from James Randi laying unclaimed for anyone who can tell the difference between cheap and expensive speaker wire in a genuinely blind test. So long as you have wire of enough guage to carry the signal and you are not talking massive cable lengths (where resistence and 'skin' effects could just start to matter) then your basic cheapo copper multi-strand (QED 42, 79 or similar) will be fine - just keep the ends clean (or cut of oxydised ends and shorten slightly) once a year or so if using bare wire connections, or use some decent spades/banana's (with some cheap heat shrink to help with keeping oxydisation at bay).
Interconnects are much the same - a well made cable is essential, but it doesn't have to be an expensive one as often the key is having decent phono plugs at each end for a good connection. I'm using ThatCable Loops at less than a tenner and they are great (locking phonos with a split centre pin so a very tight connection). I also like the basic Mark Grant G1000HD (£50) as it uses Canare crimped phono plugs at each end, and in theory a well made crimped connection with the copper wire is better than soldered connections where even 'silver' soldier is mostly tin, and tin is a rubbish conductor compared to the copper cable and plugs it sticks together so could be seen as a weak link, particularly if the joint isn't very good (as it sometimes isn't in many mass produced and rushed products).