Yea to give you a value to compare other things to, high alching right now at about 200k high alchs for the cape, at a rate of around 1k-1.1k alchs/hr, you are looking at around 180-200 hours of alching for the cape. As for cost, with the current prices at med price for nature runes and what I always like to alch, maple longbows unstrung, you are at a loss of 80gp per alch, making the cape cost only around 17-18 mil, which is actually low.
Another desirable method is to use the fire bolt (chaos rune spell) with maxxed mage gear, chaos gauntlets, sol, etc.......This is desirable because if your like me and want 99 hp, training magic and hp at same time is good. This method is only about 45k magic xp/hour (at ogres anyways) but with the added 15k hp xp, your running at around 60k total xp/hour, this method (last time i checked) was only slighly more expensive than alching to 99 magic, and it comes with a free 4.33mil hp experience, around 300-350 hours of work instead of 200, and costing around 20-22 mil. Just some ideas, GL bro!