advice on how to answer when asked to give a figure for salary expectation

worked at previous job for over 20 years so new to the job hunting. Sent in a cv last thursday and received an email from the manager the next day asking could we talk via phone monday (today).

chat seemed to go well but he mentioned that he was concerned that with my experience I might be expecting a higher salary than he could offer (he didnt disclose what it was).

he said to mail/ call him over the next few days with a figure.

Any tips on how to decide on a number

- if say my last salary was approx 50k

-there is nothing online showing salaries for other roles in the company

-similar roles to this position in other companies vary massively from 45-71k

(if successful i would have a 70km roundtrip and M5O toll daily - i know thats my problem not theirs.)

- i dont want to take less but dont want to take the mick asking for big money- of should i give a range.

thank you kindly