Seeing as how most people are looking for opportunities "online" these days, and not so much in our 3d world/face-to-face, I would think advertising a website would be most beneficial to you. I've, personally, only had a business phone number on an advertisement, along with a website though, and with both options available, I can honestly say I didn't receive one phone call. Things may be different with your income opportunity, I'm not sure what it entails, but with mine it just wasn't even needed.
Maybe text the waters a little on each front and see how that goes since your budget is small. You can see results pretty quickly if you're paying for your marketing, even with a small budget. When you see where the numbers lie, is where you finish off your marketing budget, you "roll it out" so they say.
Good luck!