Home depot has carpet below $1 per sqf. Pading is .49 per sqf for the
cheapest. Installation is $97 for the whole house plus additional charges
for stairs, furniture movement, carpet removal, etc. You can rip off old
carpets to save a little bit.
Homedepot only carries cheapest carpet in stock. To get something better,
you have to special order and it is more expensive and takes at least 3
weeks for ordering.
Costco is more expensive, price is not competitive, but I think the carpet
quality is better.
To order from local store, they may cheat you since you don't really know
what you are getting. They can show you nice sample and bring you something
different to install unless you ask them to write down the model number and
description and you check when they do the installation.