How much (roughly) would it cost to fix/replace a laptop keyboard?

I have a lenovo that has a few keys that no longer work more specifically 7-0 up on top, the letter "r" and 6,2 and 0 on the number pad. Around how much does it cost on average to either fix those few keys or replace the keyboard?

Google for the replacement keyboard. This will require your exact model number. It's likely on the order of $100 [us] for a new one and maybe half that for a used one.

install cost should be an hour of a technician's time… Whatever that costs where you live. 75 to 100 in the US

There are flat labor charge laptop repair places that may be local and may require shipping charges. Popular places charge around $100 to $150 in labor, there are cheaper.

Cost of the keyboard varies. You need to google your exact model and can replace it yourself or have it serviced.
You only state "Lenovo" and neglected to include detail. There are at least 50 different keyboards in Lenovo models over time, not compatible.
Keyboard prices, $30 to $200 probably
https://www.laptopkeyboard.com/keyboards/lenovo/thinkpad-lenovo/x1-carbon-1st-gen/
Individual keys of some models can be replaced in full kits.
http://www.laptopkey.com/BrowseKeys.php/Lenovo
Easy to break things in replacing keys.

You can get a USB keyboard for about $30.

The average price per hour for computer repairs ranges between $120 to $150. For example, a hard drive replacement could take two hours costing roughly $300.

Do you need a green or blue keyboard? JFC!

Ten to fifteen pounds. Buy one from any auction site or amazon.

Not worth fixing cheaper to use a bluetooth keyboard see