Check whether or not teaching jobs require UCAS points to employ you. I don't know if they do or not but I know a lot of graduate schemes say you need 320 points or whatever plus a 2.1 so double check if that's the case.
If it is: do the A levels because otherwise you fall at the first hurdle. Access courses don't actually give you any UCAS points so if you qualified as a teacher and then the job description said "320 UCAS points, 2.1 degree with QTS" for example you wouldn't fit the requirements.
If it isn't: Access course is cheaper than foundation year as far as I'm aware. They're about 2k compared to the 9k you would pay doing a foundation year so it just saves you the money in the long run.
Finally: if you do a primary teaching degree you won't need a PGCE. There are lots of primary teaching degrees which offer the QTS needed so you wouldn't need to do that after your degree. If you did an unrelated degree or you did something like Education Studies you would need to do a PGCE but if you can get onto a primary teaching course with QTS (like the ones at Roehampton, Durham, Canterbury Christ Church, Winchester etc) you don't need the PGCE.
Hope that helps!