Potion identification in my D&D campaigns (House Rules)

Potions and Scrolls are those one-shot magical items that can help out in pressing and troubled times. Players love them as they can shift the situation and give them a better stance towards the encounter at hand.

Everything is cool if the players create them either through a known recipe (usually known spells) or through the combined use of Craft->Alchemy & magic.

But what happens when they stumble upon a few bottled potions that carry no obvious identification marks?
The D&D D20 system allows the use of casting the Identify spell that enables them to clearly understand what the potion does, but shelling out 100 gold pieces for every potion they find can be a bit troublesome and at certain point, it may even cause them to lose all interest in trying to find out what the potions realy are (Fortunately for them a simple Read Magic spell, can identify a scroll).

In order to address this issue, I have come up with a small formula that enables them to use the Spellcraft skill, to Identify a given potion. Each use of the skill takes from 10 to 30 minutes (game time, 10 minutes per potion spell level) to identify the potion.
A player can try to identify the potion if he has at least one rank in spellcraft and failure means that the same person can only retry once he aquires at least one more rank in Spellcraft skill.
I allow a synergy bonus of +2 if the player have at least 5 ranks in the Craft->Alchemy skill.

The formula I use to get the Identification DC is as follows:
DC = 10 + potion's spell level + potion's caster level

I also allow a player with at least as many ranks in spellcraft as the Identifying person to try and help out on the identification, granting another +2 if he manages a DC 10 Spellcraft check.