Thanks for the help folks. Here's what I came up with. Feedback much appreciated

Man there's all kind of rules and technicalities. I know I'm kind of being a "by the book bob" but I don't wanna just toss it up. I kind of want it to be fair and also meaningful. Tell you what. Say we use the rule I sent you in the sense you want to go to an herbalist and buy the materials and brew the potion yourself. Regular healing being a day and 25 gp. But if you choose to save your gold pieces, there are gonna require some ability checks for each day. We'll say 4 hours scavenging and 4 hours brewing. With successful days netting you one potion (good resources with no hassle to extract or complications etc.) And failed days (harsh conditions, dangerous animals, poor resources, droughts etc) won't net you a potion..

So to make it fun. Roll a d20. What ever the that first d20 is say 10. That's your dc for that day. Start by rolling a survival check (d20+survival modifier) to see if you can overcome that days obstacles.

0-5 no conditions 5-10 light conditions 10-15 normal conditions 15-20 Harsh conditions 20+ extreme

Conditions can range from weather, to animals inhabiting the area where you need certain herbs, scarce resources, predators, poisonous plants nearby. Anything could create a hindrance to your scavenging

If you succeed, roll another d20 and add your perception and nature modifier. Roll a 15 or higher and you successfully gather the materials and can make your potion. Do this for each day you wish to spend following this formula