I frequently visit Myrtle beach and I see alot of green and red macroalgea (yellow too) washed ashore. Close inspection indicates they are in good condition (not decomnposing). I wonder if you can rinse these off then use them in the sump? They are different than what I typically seen in LFS
PS: How about sand too? I may upgrade my tank to a 240 gallon and that will save me some bucks.