Most of the testing you will use a MM for are voltage readings or continuity. Most any MM will work for those. Cheap MMs tend to be inaccurate when measuring resistance values. The good news is that the resistance values you need to measure are usually restricted to coils, and even a cheap MM can be effective, if you know how to use them. You can use the continuity setting to check the wiring harness and diodes, with decent results.
Ignition coils generally have a few ohms of resistance across the primary winding and much more resistance across the secondary winding. A cheap mm could read a dead short across the primary winding, and some hundreds of ohms across the secondary winding. Those readings most always indicate the coil is good. Also, a cheap MM will usually read voltage pretty accurately.
In summary, a good MM is only essential for an experienced electrical technician or engineer, IMHO. For your purposes, a $15 MM from Home Despot will work fine.
Note: Some Digital MMs can make checking rectifiers difficult. I therefore always liked the analog MMs best.
