The UK MOT test cost £54.85 and is now computerised. This doesn't seem to have stopped garages offering reduced cost tests, so it's well worth shopping around. Half price offers aren't unusual but it's not unheard of for unscrupulous operators from using this as a way of getting you through the door and then finding ways of failing your car and then being in a better position to get you to get them to do the lucrative repair work.
Assuming your car passes the test you'll get a Pass certificate but this doesn't remove your responsibility to keep your car legal. You can still be stopped, and potentially fined and points put on your licence, for such 'simple' things as a blown bulb or an illegal tyre.
A recent Which? report showed that the quality of MOT tests is variable, with some worrying 'fails' gettting through. With many people now tempted to cut back on regular servicing and preventative maintainance, the MOT test is sometimes the only time some cars see the inside of a garage and they're inspected for 'road worthiness'. Combing these two trends together, are you really confident about the car you're about to put your trust in ? If not, then why not find a good garage to help you stay safe and legal.
The rules on retests have changed with the introduction of computerised MOTs, with garages able to charge up to the full price of the test for a retest.