$13 on Amazon for the grime reaper. Make sure to dilute it though. A little goes a long way.
The bare bones is $13 as well and it made my trim as good as new as well as other plastics in the engine bay and wheel wells.
When you use the grime reaper, dilute it, cover the alternator, spark plugs, and other things that shouldn't get water in them with shopping bags. Then get a spray bottle, put diluted solution into it, and spray everything in the engine bay. Wait about 5 minutes then hose it down. 90% of dirtiness should be gone. Repeat if you want.