After further research into hiring I have found that it shouldn't cost THAT much but I'm still waiting to hear back from Hire for Baby and RAA since based on the monthly fees it would be closer to $700 to hire seats for both kids, which is still WAY more than I'm willing to pay. I think it's pretty unusual for someone to hire a convertible seat or a booster seat for 6 months. The capsules are regularly hired out for 6 months for less than $100 but I think most people buy the bigger seats or just hire them for a week to a month if they're travelling or something.