I use a super soil or tree soil works fine for my palms in the ground. Its just my opinoin but its gonna be while before you sabal grows its roots back and they like extra moisture around the root ball. Sand dosent hold any water and drys fast. The soil and any nutients in the soil will just help the palmetto in the long run.

A lady nursery owner once told me dig a whole three feet deep and wide and fill with 100% sand. I suggested filling the hole with pine fines and she said that would work too, because anything is better than wet, sticky clay. Personally, I have had good results with 60% pine fines, 30% sand, 10% peat.

The good thing with sand is that it is very good draining, but the bad thing is that it doesnt hold nutrients as well. I would just make sure what ever you have, it doesnt give your sabal wet feet. Maybe some sand mixed with top soil will work. Im not sure but if it still isnt draining fast enough, I guess you can also add perlite. Sabals do like moisture (as long as its not in the winter months) so it shouldnt be so well draining that it stays dry.

Good luck!