Man, Thats a pretty good price on the polk momo stuff & it is good quality the only prob. is if your putting the equip. in a c10 forget about the subs their useless.You'll need some flat piston subs like these examples
pioneer
ts-sw3041d
ts-sw301
kicker [usually a little more expensive]
07cvt12-4
jl audio [a little more]
jl13tw5
All these subs will fit behind the seat w/ it back all the way.
as far as head units go,you need to stay w/ a tried & true brand.My shop gets roped into installing cust. supplied b grade units [dual etc.]from time to time & it NEVER ends well.
You can get a quality brand head unit Like Pioneer,kenwood,alpine etc..
for under 200.00 even closer to 100.00 if you look hard enough.
I have never ordered from this site before but the sell some stuff cheaper than I can buy it for.
http://www.dealercostcaraudio.com/