My current oven just plugs into a big outlet in the wall. It's a giant three-pronged outlet. But all I need to do to get the oven to work (when it works) is to plug it into the outlet. I am now ordering a new oven online, since the old one has broken. They offer an installation service, but money is tight and I don't want to buy it if not necessary. I have people to help me lift the oven if it's just about lifting the oven, and people to take away the old oven. But will there be electrical issues to deal with, or will the new oven just have a plug and plug into the wall like the old one?
In most cases when you purchase a free-standing electric range, you'll be required to purchase the appliance cord separately. The sales person should ask if you need a 3 or 4 prong cord, at the time of purchase.
NEC Article 250.140 Frames of Ranges and Clothes Dryers. requires 4 prong receptacles and appliance cords to be used in new installations, but allows 3 prong receptacles to be used if the following conditions are met.
1) The supply circuit is 120/240-volt, single-phase, 3-wire; or 208Y/120-volt derived from a 3-phase, 4-wire, wye-connected system.
This will almost always be true in a residential setting.
(2) The grounded conductor is not smaller than 10 AWG copper or 8 AWG aluminum.
It's not likely your wire will not meet this condition (unless it's really old).
(3) The grounded conductor is insulated, or the grounded conductor is uninsulated and part of a Type SE service entrance cable and the branch circuit originates at the service equipment.
Again, the supply cable will almost always meet this condition in residential.
(4) Grounding contacts of receptacles furnished as part of the equipment are bonded to the equipment.
This just means that if there are receptacles on the range (I havn't seen this in many years), they must be bonded to the chassis (which should have been done by the manufacturer).
Plugging in a new electric range will not require the circuit to be brought up to current codes, so you should have no problem using a 3 prong appliance cord (in most situations).
It's a good idea to get somebody that has some experience with electrical work to install the cord, since improper installation can lead to injury, fire, and death. The basic idea is that you don't want to restrict conductivity in any way, so you'll want to make sure the terminals are tightened to the proper torque (a conductive paste is sometimes applied to insure adequate conductivity).
While you may be tempted to save a few bucks using the old appliance cord, this is usually not the best idea. Over time the cord may become brittle or develop corrosion, which can both lead to increased resistance, which leads to excess heat buildup, which leads to failure and/or fire. It's not worth the risk, spend the ~$20.00.
Make sure you read the manual before installing the range, and follow any and all manufacture instructions.
Most electric stoves do not include the "pigtail" cord that connects from the stove to the outlet. So a typical replacement would go something like this.
The basic answer to your question is that if you have a person or two to help you move the stoves, then the installation service is definately optional.
The first and most pressing issue is that your receptacle is a three wire and your stove will come with a four wire plug.