Profit per cast = high-alch value − item cost − rune cost
Count the item and the runes
High Level Alchemy converts an item into coins at its high-alch value. The normal spell requires one nature rune and five fire runes. An appropriate fire staff supplies the fire runes, so choose the setup you will actually use.
The high-alch value is separate from the Grand Exchange price. A profitable candidate needs enough difference to cover both the item and the runes. Alching is not a GE sale, so do not subtract a GE sale tax from the coins created by the spell.
Set up a useful comparison
In RuneMarket's Alchemy page, enter your total GP budget, session length, casting rate and fire-rune source. Fine-tune item prices and filters if you already have a buying price in mind.
Sort by net per cast to compare the margin on one item. Sort by batch profit to inspect a session-sized plan. Those answers can differ because expensive items and tight buy limits affect how many casts a budget can support.
Check the quantity before buying
Your planned quantity must fit the cost of both supplies and items. GE buy limits and your available casting time can reduce a batch even when more GP is available. Recent trading volume helps assess activity, but does not guarantee an immediate purchase.
Save a plan to a buy list if you want to track its quantities and estimated alchemy profit against updated prices. The estimate changes as item and rune quotes move; your actual result depends on what you pay.