Hi Maria, I have just done Sage Certification stage 1 - the workbooks are very good, I will be working on stage 2 shortly. I got the material direct from Sage, I think the 2 stages were £145 and they let you pay monthly. Julie
Are you the member of any bookkeeping bodies such as ICB or IAB. If so and you have a practising certificate and registered with them for MLR, best check with them, some are that you cannot offer services that you have not got qualification in - so if this is the case then may be best checking with them the courses that they accept in payroll for you be able to offer payroll services.
If you are quite confident with most softwares and teaching yourself maybe cheapest way is to buy the payroll package on ebay that is the year for whichever exam you decide on and buy past paper and go through it yourself.