It's difficult to answer this question for a couple of reasons:
1. When you're a startup -- it's quite possible your revenue will be little or nothing at first. 100% of nothing is still...well...you get the idea.
2. Every business is different -- and requires a different approach at marketing.

I'd ask yourself these questions:
1. Where do you see your startup going in the next couple of years? Is your goal to bootstrap? Is it to raise funding from VC's?
2. What marketing activities can help you get to the important threshold you're setting for your company (whether that's achieving profitability -- raising a Series A VC round -- etc)?
3. How much do those marketing activities cost?

It could be perfectly reasonable to spend $50 - $100K in marketing (or more) when you expect zero in revenue IF you're achieving other milestones that will help you achieve a Series A investment (and that's your goal).

However, if you're bootstrapping a business and your goal is reaching profitability as soon as possible, it could STILL be reasonable to spend $100K in marketing, IF you're confident that every dollar invested returns 2.

Short answer: There's no magic percentage to your question. I'd spend more time being thoughtful about the type of marketing activities you think would be helpful, and what end result those activities lead to than planning for a percentage of sales.

I hope this is helpful.