How much would it cost to have lessons (and how many does it normally take til you pass the test?
Lessons now are around £20 an hour, I heard somewhere that the average number of driving lessons needed was something like 40, this could be wrong however. If you know anyone who is willing to add you to their insurance and would be willing to take you out to practice driving (must be over the age of 21 and held a liscence for 3+ years), this will more than likely help, as you won't then waste your first few lessons getting the feel for the car and its gears. If you don't know anyone who can do this you will probably need a few more lessons.
Some people say that switching cars confuses them and they just prefer to drive their driving instructors car, personally I didn't find this to be a problem.
how much the test costs?
You will probably take your test in your driving instructors car, so you will need to pay for 2 hours of lessons (~£40) the actual test is around £35. If you need to take your theory then add another £25 or so the the test cost.
and cost of insurance?
The big one, sometimes more than your car. My first car cost me £400, insurance, if I was the main driver would have been £3000 fully comprehensive, I managed to get it down to just over £1000 (TPFT), after 2.5 years driving thats dropped to £600(Comp)
If your going to be buying your car then you will need probably around £1000-3000, £500 for the lessons, and another £2000 for insurance say. Its hard for me to give you an accurate figure because it all depends on how much your car is worth, if you get a cheap car you could insure it Third Party Fire & Theft instead of comprehensive. However cheap cars tend to go wrong more often. A newer car would be more expensive but the insurance would also probably be more.
Hope that helps