Hi harryopal and welcome to the forum.
In that price range, you will find very little advertised online. As you say you are both "mature aged", Sanur area would probably suit you, however you would have to settle for a house on the other side of the bypass (not the beach side), so maybe 5 or 10 minutes to the beach.
There are dozens of local houses in that price range, but the difficulty is finding them. You will have to drive around the area, looking for signs on walls and lamp posts or connect with some local people and ask if they know anyone with a house to rent. I'd also suggest you move to homestay in the area for a week or so, to give yourself time to look around.
You could also check on this site, where local houses are advertised. Just choose the area and your price range.
https://www.rumah123.com/sewa-rumah/
Best of luck with your search.
Edit: I didn't see davita's reply before I posted. He has given a few samples from the same website :)