Actually it wouldn't be cheaper than Strength Potions. Unlike Str Pots, you can't sell Serum 207s, so you'll be straight-up losing about 500gp per potion. In total you'll lose 950k this way. If you use your doses on the people who walk around mortton they either give you some cash , herbs or shade keys. So you wouldn't be losing as much as you think. Also the serum is a lot easier to make, as ash is very common where as limpwurts aren't too easy to get, as well as costing money. You're going to have about 1.9k potions and 3x that many doses? I don't think many people have the patience to use them on top of collecting ashes for the secondary. It is a great way for experience, I used it myself, but in terms of cost, it's more costly than other methods.