So I was trying to play some Megadeth songs on bass, and well, Symphony of Destruction was the only reasonable/easy one I could find. Anything from Rust In Peace is totally out of the equation for now, so could you guys recommend some easy 'deth songs I could start out with? Thanks!

And Ellefson is one tight player.
Try out Countdown to Extinction, Dread and the Fugitive Mind, Trust, Disconnect, Return to Hangar, She-Wolf, Dawn Patrol. Just keep working at it and eventually you'll be able to tackle the Rust in Peace songs. I was in the same position you were a couple years ago and now I can blaze through most of RIP and its very satisfying.