For budget version:
[card]Fel Reaver[/card]s are interchangeable with [card]Clockwork Knight[/card]s. You can play 2/0 (FR/CK), 1/1 or 0/2.
[card]Archmage Antonidas[/card] is a secondary win condition, but it’s also not necessary. You can probably play a [card]Loatheb[/card] or a second [card]Unstable Portal[/card] if you don’t have it.
[card]Dr. Boom[/card] can’t really be replaced if you want the deck to be successful. That should be the first Legend to craft. If you don’t have it but you still want to play Mech Mage, just like above, Loatheb or second Unstable Portal.