Underfloor safe is the best option, I fitted one at a previous place, most have a recess lid, making removal from prising almost impossible.
At the lower end of prices for underfloor safe , have a 2k cash, valuables 3k- 4k rating, around £150 will get you a 225mm - 300mm square safe.
A higher quality safe like a Churchill D2L Underfloor Safe with a 4k cash rating, valuables 4k about £280, modern underfloor safes are fitted with a round locking door, not the old fashion square door.
A bit of work installing one, but it's secure, no one isn't going to run off with it.
And don't buy one locally.