lala - it will depend on how much cover you want, your age, health history, whether you smoke etc. The cheapest way is to get fixed term, eg 20 or 25 years to cover you until the mortgage is paid off, children leave home etc.
You can get rough quotes from all sorts of online places - just google life insurance - but prices will vary slightly depending on personal circumstances (and you may not be able to buy online if you are not in the UK). The tesco insurance page gives an example of a 42-year-old man with £307,000 of cover over 20 years for £34.71 a month - if you're younger and want less cover obviously it will be cheaper.
Can I also say from experience that you should both be insured. DH died suddenly at the age of 41 leaving me with two small children. If we hadn't had substantial life insurance I would suddenly have had to go back to full-time work to pay all the bills, at a time when the children needed me to be around more, not less.
And even if you are not working, you only need to think of all you do in terms of childcare and household stuff, and how much it would cost your DH to pay someone to do it all, to realise that it's a good idea for both partners to be insured.