There may be a bus direct to Torrevieja by then. It should have started in March but it now looks as if it is dependent on whether the new bus station is built. You might be lucky and the bus service will have started but you still won't be dropped off in Quesada. All the buses from Torrevieja stop at San Luis so you'd have to get a taxi from there, anyway.
(Sorry about all the might's, should's, may's etc but the service was promised, honest)
I'll ask around my neighbours and see if anyone is going there on that day and will let you know. You never know, you may be lucky.