I've recently had a bunch of car issues...

Long story but will try to sum it up.

Car seemed fine on the Wednesday, Wednesday night I tried to drive and it had very little power, I couldn't get over 2000rpm and then about 100 metres up the road, all tyres locked up, I skidded, and then car resumed driving.
Still with very little power, but was drivable, if very slow.

I phoned a mechanic and explained the issue. He said gearbox.
I posted on these very forums. A few people said gearbox.
I phoned other mechanics. They said gearbox.

So after saving up $800 (cost of gearbox and fitting as quoted by my mechanic), I booked the car in.

Got a call during the repair to say that my CV Joint passenger side, had died... Bought a replacement part, delivered it.

Today they told me to come get my car. I got in, started it. No power. No pull. I drove put the driveway and all the tyres locked up.
So $800 later, the problem isn't fixed and it clearly wasn't the gearbox OR the CV.

They now say it sounds like broken speed sensors. 2 of them?
There's more than one?
I've never heard of them before. But after my boyfriend had a go at them, they agreed to source and fit the speed sensors free of charge, but still...

Anybody out there have any ideas?

If the car has ABS there are sensors in each wheel hub to detect wheel rotation differences. If the car also has TCL (which shares the same sensors), the loss of power you report could be a result of a problem with one or more of the sensors leading the TCL system to reduce engine power. A leaking CV boot can cover the toothed wheel that the sensors monitor with grease and other rubbish which makes the sensors produce inconsistent signals. If this is the case, cleaning the toothed wheel and sensor should restore normal operation, unless a sensor has been damaged. You should have some sort of warning light (ABS or TCL light flashing) if these systems are detecting a problem.

The above sounds like a pretty good explanation. Quite why those cowboys assumed it was the gearbox is beyond me. If all wheels lock up, it's clearly not a gear problem. Looking at systems which link all wheels to lock up would lead us to assume it's the ABS system. I'd also be demanding some of your money back. And please do name and shame them.