Peppy,
likely the frame is the same. the only difference would be the gears, hubs, rims, forks.
like all things, you get what you pay for. if you're just using it for street riding, get the basic one 690. probably the only other factor is the hubs/wheels - if they all have same hubs/rims then go the cheapy, but if the next model up has better hubs, get that (cheap hubs are much harder to push than not so cheap ones
)
if you're doing some trail riding, the more expensive bike would probably be better value for money. hard to say without knowing the nitty gritty...
