Jean I buy my BP from Chemist Direct - a tube costs less than £5 but lasts for about a month. I tend to buy 3 tubes at a time to save on postage.
As for my regime, I do the following:
Morning - I wash my face in the shower with Boots No 7 foam cleanser, then put Boots bog standard day moisturiser on.
Evening - Wash my face at the sink with No 7 foam cleanser, wait for it to dry for a couple of minutes then put BP on my chin/jawline/neck. About 10 minutes later (you can feel the BP drying out), put Boots No 7 bog standard night moisturiser on.
I follow the acne.org advice of using foam cleanser, gently rubbing/patting the cleanser/BP on with the tips of your fingertips and gently patting my face dry with a towel rather than rubbing.
Once you get into the habit, it becomes second nature tbh.
2 tips though - go very easy with the BP at first and build it up very gradually. I didn't and had a very red and flaky skin for about a week which was very
- the only time the flakiness flares up now is when I start a new tube but it is nowhere near as bad as the first time.
Second tip - it is bleach so be careful what you touch with your face when the BP is on. As I tend to do my evening routine around the DC's bathtime, most of their PJ's have bleach marks around the arms/shoulders as I obviously touch them without thinking before they go to bed 
hope that helps 