Note: This would have to be in conjunction with moving Spell Vamp's stacking to something like the flat movement speed from boots, and Tenacity - a global uniqueness.

Recipe: Boots + 1250 = 1600
Stats:
Enhanced Movement 2
1% Spell Vamp per Level
(Does not stack with other boots. Does not stack with other sources of Spell Vamp.)

Spell Vamp is currently missing from the AD caster niche (lol, intentionally, probably...), and I think it would be nice to have on champs like Talon, Riven... Talon... Riven...

Anyway, Having 1% spell vamp per level means that around upgrade time they will only give 4-6% spell vamp, and at max levels they will only give 18% spell vamp.

That might be interesting, especially for the cost. Scaling the Spell Vamp on your level also makes it a risk-reward kind of purchase.

The problem I see with implementing it as I put it would be that nobody would buy any other boots... except like, carries and tanks...

I feel like you can allow the combine cost to be 950 if it's going to scale by level and not be a flat amount.

I'd rather see spell Vamp broken down into a base item equivalent to vampiric sceptre, and take its place in existing and New recipes. Spell Vamp boots would be very effective, but at 1600 gold, you can nearly buy boots and hextech revolver... If the root of the interest is spell vamp for AD casters... I think a better method should be pursued...

Talon...Riven...URGOT
Also make it a little more expensive and give it 1.2% spell vamp per level and we good. It gives straight casters more diversity for boots. Spell Vamp? Magic pen? Cool downs? an it makes Urgot slightly more viable which is a plus for everyone.