Hi Danielle.
Subscriptions add-on supports setup fee for the plans. So you can achieve what you want by following:
1. Create 3 plans (for $100, $200 and $300 respectfully) with $900 setup fee (your base product price) each.
2. Attach these plans to your products.
3. Create a page where your customers can select the product they want. You can place 3 product buttons on that page using shortcodes (or attach them to existing buttons).