Why not sell the hybrid and use that money to go towards the new road bike? Also, explain how a good road bike can last many many years. It's not like you are going to buy a new one in a year. Okay, you may want to, but you don't NEED to. What are the alternatives? Joining a gym....that's not cheap. How much do you spend on vacations? A decent vacation can easily cost over $1000, and I bet she/he doesn't flinch at that.
Is it that you can't afford it, or that she/he thinks it is overpriced? There is a big difference.
Perhaps you can negotiate a deal where you skimp on other things you enjoy to justify the expense. I delayed getting a new car to get a new bike. Seems silly, since the new car would be $25,000 and the bike cost me $800(my brother works at the bike shop). Also, can you commute using the bike? You could justify the expense by saving on gas. Let's see my gas expenses are at least $60 a week. If I rode instead of drove to work, I would save $2600 in a year. The bike would easily pay for itself in just a few months.