It should be enough to cover a year, but there are some things you should consider.
First, Guinea pigs have an average lifespan of 5-7 years, so you will have to be prepared to financially support them and care for them for that amount of time, whether it be getting a part time job throughout the year, or saving every summer, etc.
Second, you should really get 2 pigs, not just one. Based on my expenses (it will probably differ depending on where you live, etc) this is what my pigs cost me per month:
2-3 bags of hay at $20 each = $40-$60.
1 bag of food at $20 each = $20
Veggies (paid for by my parents) ~$15-20
Bedding (If you are going to use shavings) $20 each bag (4-5 per month) = $80-100, however with these cages many of us use fleece and towels, which is MUCH cheaper, as you just throw it in the washing machine once a week instead of buying more shavings.
=~ $75-100 per month (~$200 including shavings). There are cheaper alternatives for hay if you have a local supplier that can proved timothy hay by the bale, you just need to have somewhere to store it (i don't). You can also order Kleenmamas hay online by the bale, and I've heard good things.
Now for startup costs, for the cage etc, these are my estimates:
Guinea pig adoption fee: $15-$40 each (Not from a petstore, search petfinder and craigslist, or local animal shelters)
Coroplast: $15-30
Cubes: $15-40
Accessories: ~$40
Fleece and Towels/Mattress Pads/Uhaul blanket: ~$50? I don't have a good estimate of this, I got mine for free.
Total for the startup: ~$120-160 altogether.
I also discovered recently it is a good idea to keep a vet find aside for emergencies. Where I live a vet visit is $40 plus the cost of medication, but that differs depending on where you live, I know some that charge $70 plus medication, so it's best to find a local vet that REGULARLY treats Guinea pigs, and ask them for an estimate.
Keep in mind that this is just based on the costs in my area, so hopefully it sheds some light on how much you will need to spend on these critters. It's easily doable though. I got mine when I was your age, and have managed to pay for them with a part time job, working on weekends and holidays.
Good luck!
