My shift key is not working anymore ;-;

The rubber dome or keyboard matrix has failed, and you will need to replace the palmrest assembly, sad to say - the keyboard is not modular so that does increase the cost.

The main reason cost is a problem with Chromebooks is they have update expiration dates; once it's expired, they depreciate off of a cliff in seconds after it's official. Older ones were EOL in 5 years, newer ones tend to last ~6.5-7 years, depending on if it's EDU or non-EDU and how long Google decides to support it. As such, you need to check used machines closely.

The problem is this Chromebook “expired” in terms of updates on June 2019, so it has been 16+ months since it went to unsupported status. If it doesn’t bother you parts tend to be cheap for EOL Chromebooks because of ones people stripped for parts and “as-is” ones with an enterprise lock that wasn’t removed, so you can get creative with finding the part and have a good shot at it if you need to do that. That said, you may want to at least consider a newer model with a few years left if the repair cost is similar.