Seconded. I'm on these at the moment and they even you right out. They're on special offer at Holland and Barrett at the moment - 120 for about 15 quid. Enough for 60 days.

Also, to be massively pedantic, 5-HTP (5-hydroxytryptophan) is not an amino acid, but a derivative of the amino acid tryptophan and the precursor for serotonin (5-hydroxytryptamine). It basically boosts the brain's supply of serotonin, but a way that doesn't make you go mental - it's up to the body and its supply of enzymes how fast it'll convert 5-HTP to 5-HT, so it's not like taking speed or anything.