Like mtk said, It is quite simple to diy if the will is fairly straight forward as I did it myself when my mam died, I was the last left the baby, lol the udders long gone and married, but house left to me as there was nothing else, and I was named as exector on the will, and that was a home made will which I copied from a will book.
Sum up: if it's straight forward, then do it yourself. Take your time, no need to rush, it does take a bit of time. good luck.