The words "Bristol" and "affordable" are seldom used together....
But "Bristol" and "very enjoyable" - yes!
If I may advice, I would look for the best possible example, as a proper restoration is quite expensive. The driveline is not expensive to restore or/and upgrade, but specially the interior is. Instruments, seats, the tubular construction beneath the Aluminium skin, all windows ( specially front and rear), hinges, lights etc are not easy to repair or source.