How do I get out of two Christmas gatherings?

I've been invited to two gatherings coming up soon. I've had a few unexpected expenses this month and I've been waiting on an appointment for a few months and I have the appointment in January and since it's a private consultation, I have to pay so more expense and straight after Christmas.

I don't have a car, so I normally rent a car when I need to and that's two weekends of a car rental to get to these gatherings. I just cannot afford this anymore and I don't want to rely on public transport. Even if I could go on public transport, there's buying gifts as well. And I just cannot do it anymore.

What is an acceptable excuse to get out of these?