Depends on your budget. I remember quite awhile ago reading into the KJW M700 gas rifle because I was on a tight budget.
Paired with a DBC tight bore barrel (which I believe is the only company that makes the correct size for it) you have an accurate rifle shooting ~500 fps. Maybe you'd want to use a propane rig with it as well because I hear there are problems with the natural lubrication from green gas with the internals of the rifle. Total you'd be looking at paying ~$300 for a fairly accurate and powerful rifle, of course you'd have to factor in the price of gas, etc.
On the other note:
Training with any firearm will always help your accuracy in the future but there are too many other things to factor in when going from air soft to using guns. Real firearms fire at a much higher velocity, use ammunition that is much larger, are very loud, have a lot of recoil, etc.
You don't need to buy a firearm to shoot them, look up local shooting ranges, head over with enough money to rent a gun/ammunition of your choice and the hours you plan to stay there and tell the staff that you've never fired a gun before and (most of the time) they won't have a problem helping you out.
Either that, or pay some money to take a course (usually done by NRA instructors and cost a small bit of money).
