Transponders, Radios and other avionics procurement questions

I'm at the point where I need to start collecting instruments so I can
build the instrument panel.

As always, I'm a bit shocked at the prices new or reconditioned
instruments cost: The typical panel mount radio goes for around $900
to $1300 depending on how much power and features you want. The
transponder can be around that price too.

Here's another question about the transponder: Must it be coupled to
an encoding altimeter or can it get it's altitude information
independently of the altimeter? Or does that depend on the
instrument?

Speaking of the transponder, I have flown enough to have an opinion on
what type of instrument is easier to operate: Those that allow you to
punch in the squawk code one number after the other. The types that
force you to dial in the first number, move the curser over and dial
in the next etc etc do work, but it's cumbersome and adds to the work
load to have to decode the instrument so you can operate it. So given
the choice, I'd prefer the types that allow you to dial each of the
four numbers independently, or those that allow you to punch in the
number off a key pad, one after the other.

For the radios, having both active and standby frequencies showing
just makes good sense and lessens the workload.

I've found what appears to be a pretty good source for the standard
instruments in but haven't asked him yet if he also handles avionics.

I'm new to this part of building so any ideas or locations or sources
are welcome.

Thanks, Corky Scott