I want to gain weight?

Hi my name is Adam. As of right now, I weigh roughly 120 pounds. I played football 2 years ago and back then I weighed 145. I have lost 25 pounds since then. I sat around the house for 8 months straight which could be the problem. Recently I have been working out every other day with a good buddy of mine and he is training me. I also am going to try and use some protein shakes. I am going to try GNC weight gainer 2200 but there is only 5 servings in one jug. And it is a very large amount of powder and it is extremely expensive for just 5 servings. Is there any way for me to gain the weight I used to have? And gain muscle as well? I just don't have that much money and I don't want to spend 30 bucks on something that only gives me 5 servings each time. My metabolism is very high so I have always struggled with gaining weight. I am tired of being so small and I want to look bigger by the time summer time gets here. So any advice would help. Please let me know. Thanks.