e21 will not start
 

The solenoid will click once then nothing. If I turn the key off, wait a minute or two, then try again, it will do the same thing.

Do I need to replace the solenoid and/or starter, or is there something else I can do? Looks like a real pain to replace:(

Check your battery, make sure it's fully charged?

Yup, battery first. Anything less than 12.45 volts and its most likely dead or to discharged to start the car. Two things, if it has juice get a WOODEN broomstick and have someone thump on the starter while you try to crank, occasionally this old redneck trick will get the solenoid to pop loose and work a bit longer. 2, make sure the battery light on the dash is functional (when in doubt just replace it, its less than 3 bucks for a two pack), if its not working the alternator will not get a signal and will not charge your battery, hence a potential reason your battery may be dead. Good Luck