Does Rell, Magnetic's gear discount check the gear's current cost or its printed cost?

No. Rell is looking for gear with a printed cost of 2 or less — abilities that reference a card's cost always look at its printed value, not any discounts or increases currently applying to it. Even with Ornn's Forge's discount active, a 3-cost gear stays a 3-cost gear for the purpose of that check.