3 hours flying a 747-400 sim.....
I don't wish to know the merits of that, but you really will be struggling with that.
If you want to fly a 737, you would be better off doing a JOC course on the 737, there are providers out there who use the sims at Gatwick (Gecat/Oxford), Heathrow(BA's Cranebank), these are the same type you will use in your career, they will help you in your first type rating.
Is the cost worth it? thats up to you.
best of luck.