Well, being a college student I’m assuming you’re probably at least 19, in which case you started training at at least 17. Going from 115 to 165, provided it’s not a fat 165, is already a great accomplishment.
If it’s a lean 165, then this sounds somewhat like a case of “if it’s not broke don’t fix it.” Whatever has worked for you to accomplish that, if that’s the case, is obviously not bad, though perhaps it can be improved yet further.
On your general question, there’s no reason to increase caloric intake by more than 1000 per day over what has been maintenance. Actually that is usually too much of an increase, at least over an extended period of time, but is reasonable for shorter periods.
Hopefully you’re already getting solid nutrition at least six times a day already – not every one has to be a meal, some could be meal-replacement product or that plus some small amount of food. If that’s not the case, and instead you’re going more than 3 hours at a time with no food, I’d look first at improving the frequency of eating.
If the frequency is fine, then all it takes to add 1000 calories per day is to add about 167 calories per meal if six meals per day; even less if it’s more. That can be accomplished with nothing more than a scoop or two of a protein product, or with quite small amounts of any nutritious food.
Precision and diligence will easily do it, only exception being if an eating aversion occurs due to the amount simply being too much.
On the other hand, I would certainly make an effort to measure bodyfat before assuming that eating to gain say 10 lb in the next few months is a reasonable goal, or if instead it might not be better to drop 10 lb of fat and then gain the 10 lb (or whatever) of muscle.
On the cost, personally a favorite source of added calories and nutrition is a Hungry Howie’s pizza over the course of the day. About $8. Actually that’s 2080 calories, 122 g protein, 253 g carbs, and only 21% calories from fat (at least this is the standard; some individual franchises are greasier.) So half a pizza, five slices, would give you that 1000 extra calories at a cost of about $4. I haven’t compared costs of MRP’s so I don’t know if they are less or more, probably more.
Other choices include adding for example lower-fat cheese, or as slickid said, eggs. Eggs are a fairly inexpensive source of protein. A dozen eggs per day is about 840 cal and costs under $3 (there is no problem with blood cholesterol incidentally, as shown in a study by the American College of Sports Medicine finding blood lipid profile to improve with increasing egg consumption up to the limit studied, which was 12 per day.)
