Free 'basic' versions and paid 'pro' versions of software are very common, so it's definately _possible_ that it could be viable. If you want to get investment you'll have to make as convincing an argument as possible that 1) in your hands, 2) with your product, and 3) with your market, it _will_ be viable. The more convincing the argument, the more likely you'll be able to get investment.

That means getting some preliminary data (which can take many forms) which makes a convincing argument. See the examples below:

Not a convincing argument:
"This other company did this and made 10 billion dollars".

More Convincing Argument:
"In our pilot program, X% of our free users with company size Y ended up converting to paid advanced options, and here's a graph of the increasing rate at which we're able to recruit companies of size Y to the free program."

If you'd like more tailored advice for your specific product, send me a link to more background info and I'll look it over,

best,

Lee