Handguns:
USPS allows this shipping method by FFLs only.
UPS requires overnight for all shippers
FEDEX requires overnight for all shippers
Receivers, Rifles, Shotguns:
USPS, UPS, and Fedex allow standard shipments
On the handguns, UPS and FEDEX requiring overnight service is a company policy not a law. If you follow that policy the overnight saver is the cheapest method, this is one that gets there by end of day, not in morning. The cheapest way by either carrier if you are following their policy is UPS next day air saver with your handgun packed inside a UPS shipping box. If you are not following their policy, you can ship your handgun UPS Ground, etc very cheap, you would breaking the policy of the carrier but not any laws that I am aware of. If your workplace, etc has an account UPS discounts around 40% on overnight on accounts, the ground discount is closer to 10%.