I was thinking about getting another upper for my Bushy, but all the ones I look at are about the price of a new rifle.  where do you guys get your uppers?

Garrison (on the EE) is a good source for non-ramped uppers and LMT (sold by MSTN) is a good source for ramped uppers.

I'ld get M4 ramps for anything shorter than 16inches.  

this is not an immediate thing(i dont have any money right now), but i have a bushmaster varminter, which is great, but its so long and heavy...i want a light carbine with iron sights for fun

Honestly, I like buying a good used upper on the EE and when I decide I want something different I just sell it again...  There are always a few really good deals on there and both you and the seler win....

I agree with Troy, but I find few things more irritating than a suprise when you pull the trigger.  Going cheap has been a journey of pain for me.  I also don't have enough money for a separate knock-around upper. ;) So I would recommend getting a quality one.  Plus, it's usually little trouble to get the features you want, compared to adding them later.  
If the rifle is a Bushmaster, and you are happy with it, look at a lighter upper from the same company.

i just ordered a rra 24" upper for $350 shipped from rb precision.