Outdoor Spa

Hi
We are thinking about getting a small outdoor spa for our small backyard. We have had an above ground spa before and all you needed to do was change the power point. But this time would like either a 1/2 sunk above ground (in cabnet) or a shell one.
Can some one tell me how this works. The lady in the spa shop said if you sink a shell in the ground you have to go gas, is this right ? if so any ideas how much it costs to connect fom the house ?
If we 1/2 sunk a portable spa, how do you get to the pump etc?
Very confused
Any advise would be great
thanks

a friend of ours has had 2 spas and at least one of them was electric/ possibly both. They were both the shell type not cabinet and were half sunk into the ground.
Her first one was a 2nd hand one bought from her sister and BIL from when they were selling their house. The second brand new when she build a new house herself. Both in Perth.