with our tunes you are likely to see a good bump in mpg. Almost everyone is reporting better mpg, and the bigger turbos are actually a bit more efficient than the stock ones, so that is also going to help with MPG.
These turbos are not just some "bolt-on" bigger turbos. They are built in toyotas factory directly, consulting with the engineers who designed this engine.
The design is made to maximize power on stock engine without any additional risk and without increasing turbo lag.
Install cost for us (at a toyota dealer) was about $5k, but it included other things, not just turbo swapping.
I'd budget $3500-4500 for install cost.