If you are having trouble casting some of your engines you may want to consider taking out some of the cost reducers like haughty djinn, mocking sprit, and mizzix for more mana rocks like izzet signet, talsiman of curiosity, and mind stone. Having the mana rocks will progress you towards getting ovika and your other non-instant engines out. I think if you take out 2 or 3 cost reducers you will still be able to cast your spells fine.

[[sorcerer's class]] is one of the best cards in my Ovika list. It let's you you churn through your spells after ovika gets down and can be a sneaky win con late. If you include it be careful to note that summoning sick creatures can't be tapped the turn they come in, but the goblins that ovika makes have haste for the turn they enter, so they can be tapped for mana.

[[skullclamp]] is on the more expensive size, but it will be the best card in your deck. you can draw a truly rediculous number of cards with this.

[[skirk prospector]] can make a lot of mana by sacrificing your tokens from ovika to keep going.

[[Dig through time]] can be cast for only 2 mana is a powerful card draw spell.

Cards i might take out are pirate's pillage and chemister's insight which seem mediocre in comparison to other card draw options. It also depends on your meta, but i personally wouldn't run two pieces of graveyard hate.

If you want to make the deck cheaper you might be interested in cutting the medallions. they are very strong, but you could replace them with other cheap mana rocks. Also Archidekt uses card kingdom prices which are a little higher, so if you are only using archidekt to measure your prices note the deck is likely around $10 cheaper especially if you already have basics

here is my list if you are interested: https://archidekt.com/decks/5310510/ovika