Weight lifting with not too much to lift?

I am done both of my baseball seasons and I was looking to start gaining some muscle. The only problem is that I can’t get to a gym until school starts, and even then I don’t have weight training as a class until January. I have very little weight lifting equipment-2 lb dumbells, 3 lb dumbells and two sets of adjustable dumbells one up to 20 lbs and the other up to 40 lbs for each. Anyone have suggestions of what I could do with these weights, or body weights. Also does anyone know how much a barbell costs and where I could get one.

Dicks sporting goods runs there 300lb olympic weight w/ bar set for $109 quite often, that’s considerably cheap as far as weights and olympic bars go.
Power racks run upwards of $300.

Here’s a workout you could do you just need 2 milk jugs. http://www.teenbodybuilding.com/derek22.htm

I don’t know how effective it would be for gains but I would think it would help you atleast maintain what you’ve gotten.