Currently that's 1500*0.00037000*2558=$1419.69 in a month. With a low rent you can live on that full time. When KMD rises and multiplies that sum will also rise and multiply. After the BTC event coming up BTC could rise to up to $4000/BTC this year. It was originally stated that they should get about $500 each month "get the ~$500 per month". When notary node operators dump KMD and profit in BTC and then in $$$ the KMD rate decreases.

https://support.supernet.org/support/solutions/articles/29000010574-notary-node-elections