Question: I've been looking at [the cards from Dominion: Alchemy](http://dominion.diehrstraits.com/?set=Alchemy) and want to use some of them in my own games through proxying of the blank cards. However, I don't feel like delving into the whole potion thing, especially since it would be annoying to have to proxy at least 4 different cards (the potion and 3 kingdom cards to get the recommended amount of 3-5). So I figured I'd just give them costs in $ only and not potions. Another application of this might be playing with the alchemy cards if for some reason you didn't want to use potion as well. 

However, I'm not exactly sure what costs to use. A potion is roughly equivalent to a silver, but that seems like an oversimplification. One of the interesting things about alchemy is that you have to [buy the potions in order to access these cards and balance them with your other currency.](https://boardgames.stackexchange.com/questions/3116/how-does-the-addition-of-the-potion-treasure-from-dominion-alchemy-change-the-ga) This scarcity makes me lean more toward counting a potion to add +3$ to the cost. 

Does this seem about right? If not, could someone perhaps provide a case by case basis for the 9 cards this would pertain to (since Alchemist in a potion-less game would be rather odd I'm not planning on including it)?

Answer: 
I agree with the other two answers, but I have a little more to add, so since you haven't accepted an answer I'll throw in my two cents.

The point of potions in the cost isn't to make things cost *more*, it's to make things cost *different*. (The re-shuffle delay is also a good point.) If you want a potion card, you need to invest in a potion that won't be useful for other things. By just increasing the cost, you lose this. In games with a few Alchemy cards available, the decision to buy potions or not usually depends on the variety of potion-costing cards available. While Alchemist can be a strategy in itself and a Familiar might be necessary early on, I probably won't buy a potion to get Vineyards unless there are other potion cards I want as well.

Because of this I agree strongly with @philosophyguy that, if you're proxying, just proxy the potions as well. However, if you *really* want another mechanic, I think adding 3 to the cost would not work well. For Familiar, 2 is more appropriate (equating it with Witch). However a University or Scrying Pool for 4 would be ridiculous in many card sets, they would need to be 5. But I think there needs to be some sort of other cost mechanic.

Perhaps require trashing a (non-copper) treasure card at the end of your buy phase. It could work reasonably well to make trashing a Silver part of the cost of the 2P and 3P cards, trashing a Gold required for Possession (and maybe Golem?), though I don't know how to extend this well to the 0P cards.

This solves the reshuffle problem adequately; you'll need to buy a Silver in your first 2 turns to get a potion card in the next two. Not being able to re-use the "potion" (can't trash a Silver more than once) is somewhat balanced by being able to use the Silver for other things first. I think it would be playable. It will still change the strategy however. With potions, you have to make a conscious choice in advance (buying a potion) to make the potion-cost cards accessible. With any other mechanic I can think of this is lost, and it is possible to buy a single potion-cost card on a whim.
Honestly, I would just proxy a pair of potions. Potions are different from normal treasures in that each player often will only buy 1, whereas a typical game will have multiple purchases of Gold and Silver by each person. So, making the Potion proxies does not require as many cards as Kingdom card proxies.

If your goal is to just play through the cards to see what it's like, why not take a stack of Kingdom cards that aren't being used in a particular game and pretend those are Potions for the game? I would recommend having a reminder in large letters for everyone to see so they don't accidentally play their "Bureaucrat" as a Action rather than as the Potion it's representing, but that would be a simple way to try out some Alchemy cards.