I'm not a big fan of tattoos, but that doesn't mean I don't approve of others getting one.
Like someone else posted above me...set aside maybe 10 dollars per week until you reach your goal. That way you can still pay for other items you need without running on empty at the end. This is also good practice for later in life when things suddenly need to be fixed unexpectantly or for emergencies.
As for what you should get? Seeing how you love your kitties, why not get something to represent them? Such as a paw print as someone already requested. Or something that is meaningful to you. Just remember, once you have it, you can't take it off, or at least it will be very difficult.
Also, this is the most important. Go around to different tattoo parlors and see how clean they are and how safe! Do not go to the cheapest or the most expensive. I would also get recommendations from their clients and make sure they sterilize everything. You do not want to end up with an illness from unsafe practices.
Good Luck! Let us know what you decide to get!