I'd assume you apply the feat first and then the booster since the feat is a permanent effect that changes your range.
So they do stack and your range is 120ft.
the Psychic Booster also calls out all telepathy, whereas the feat calls out Limited Telepathy specifically. So my instinct is to apply the specific one first.
Extended Telepathy isn't a multiplier though, it's a static addition. It doesn't double your range, it just extends it by 30ft.
I'd also assume you add static bonuses before multipliers as well in cases like this.
And yeah, 30ft. range increase on limited telepthy is rarely gonna matter. And when it does i'd be very surprised if it breaks the game.