You can get Io items for free in the . The fastest way is opening — noticeably cheaper than buying on the market.
The cheapest Io item costs $0.30. Prices update based on the Steam market.
The DotaLoot database has 7 items for Io, prices from $0.30. Rarities: Mythical, Legendary, Arcana. Any of them can be won from DotaLoot cases or claimed for free in the daily giveaways — noticeably cheaper than buying on the market.