Hi - can someone please help me?

My car is the crossfire 2005 ... the problem -
Has been getting worse -
Originally it just didn't start - happened once .. so thought no more of it .. as it started about fifteen minutes later
2. A while later .... about six months - the same problem - this time i had on road assistance start it ... the mechanic did a sequence of things ... remotely unlocking and unlocking .. then putting it in neutral etc etc
3. in the last 5 weeks - the car stopped while i was driving ... electronics still on.. but motor died .... it started again immediately
4. next time it stopped ... same thing - electronics still on .. and did not start immediately - called road side assist ... car started while i was waiting for them
5. next time it stopped - same thing ... electrics on dash showed on .. but engine did not turn over
6. next time it stopped - and would not start ... so had it towed to the mechanic.
7. the dash light has continually had the oil sensor light showing ... even after a service ...
8. The mechanic has called to say that the oil level pressure sensor is not working and needs replacing for AUD $1100\

I have been looking at people with similar problems ... where the engine died ... then did or didn't start, yet the dash had electrics on.
I have seen on the forum people saying things like - crank shaft sensor ... relay control module and a couple of other things were the problem

Help me please? $1100 is a lot of money to spend and not know if it is actually the problem ... what do i do?! From a Crossfire lover - i really do love my little car .. but she not drivable and this is looking expensive ... from NasF1