I2C - switch scl line
Assuming you're in a single-master situation, using an IC like the TS12A12511, a single SPDT switch would let you do this with one extra I/O pin:



MCU_GPIO controls which one you talk too -- I assume you don't need a 'float / no-connect mode'. The on-state resistance of this switch is ~5 ohms, which is virtually nothing for I2C. I assume that your I2C bus runs at the MCU voltage, so you should tie that to the V+ pin on the switch. The part can slew rail-to-rail, so there should be no problems there.

I would then also place my I2C pull-up resistors on both SLAVE_0_SCL and SLAVE_1_SCL -- this prevents floating input pins at the slaves which can cause undesired behavior, which would be the case if you left the SCL pull-up on the 'MCU_SCL' side of the switch.

I don't know what your quantities are, but this drops to about $1 at 100 pieces.