Muldrotha, the Gravetide | Combos (EDH / Commander)

I would love suggestions on how to make this deck better. I'm trying to keep it budget, so no really expensive cards. It's a somewhat control-ish deck that just wants to wait it out until late-game when it can combo off and win.

I particularly would like some more wallet friendly protection cards (to replace Glen-Elendra Archmage & Sylvan Safekeeper)

There are various ways to win:

1. Get infinite mana, play Walking Ballista, and win. If you don't have Walking Ballista in hand or in grave, cast one of the spells under "Drawing Library" and cast it for X=exactly the number of cards in your library. Then, play Walking Ballista and win.
2. Get infinite mana, cast one of the "Drawing Library" spells, cast it for X=exactly the number of cards in your library, play Laboratory Maniac, play Gitaxian Probe, win.
3. Play Devoted Druid, Quillspike, and Jarad, Golgari Lich Lord. Tap Devoted Druid, place a -1/-1 counter on it to untap, use the 1 green mana generated to pay for Quillspike's ability, repeat. When Quillspike is huge (greater than the life of your opponents) sacrifice him to Jarad, Golgari Lich Lord, drain your opponents' life, and win.