I think this is a good price for a frame lock; frame locks are low security locks for quick stops to prevent the rear wheel from turning and someone riding off with your bike.
This requires eyelets near the rear wheel to install. Not many bike frames have these but are more common on dutch style commuters.
I've been using one of these for a couple of years and find them really convenient. This model lets you remove the key when unlocked.
also consider aliexpress, given these are low security.
https://www.aliexpress.com/item/1005007387508989.html
https://www.aliexpress.com/item/1005005496207661.html
Second one has pic with it attached by hose-clamps to a standard frame :-)