A few bottom line thoughts.
It is more expensive to build a kit than buy an ARF but when building the cost can be spread over the time it takes you to build.
On the cheap a good nitro trainer and field gear will run around $400+
If the budget is real tight there are plenty of used trainers out there for under $100, I have even seen trainers given away through our club (I gave a brand new trainer to a kid down the road that was given to me) Keep your eyes open for these deals.
Flying in a cow pasture should be no problem if it is big enough but it may tick the cows off.