Random idea: Magic Spike: what level should this be?

[qwertyu63]

Magic Spike
Abjuration
Level: Clr ?, Sor/Wiz ?
Components: V, S
Casting Time: 1 immediate action
Range: Close (25 ft. + 5 ft./2 levels)
Target or Area: One spellcaster
Duration: Instantaneous
Saving Throw: None
Spell Resistance: No

You can use magic spike to disrupt a spellcaster as they are casting a spell. The spell they are casting is counterspelled. They may sacrifice a spell slot of any level (using it up for the day) to negate this effect.

[Fosco the Swift]

Considering that its like a very specific "Dispel Magic", I would say its 3rd level.

But the no saving throw, no spell resistance and an immediate action gives it advantages that no 3rd level spell has.
Then again, it can be simply negated by a 0-level spell.

So if you want to make any changes, I'd say a 4th level spell that is only negated by a Spell with a Spell Slot equal or greater than the spell being Magic Spiked.