I have been offered a 7730 new for HKD2000 or used for HKD1000. Which should I go for? Neither has a warranty but I know the seller. To buy new from the shop would cost HKD3500.

go new -- 7730 has painted bezel around the screen and it gets worn out...atleast let it get worn out by your sweat, not someone elses.

Noted. Does the 7730 share the same charging requirements as the 7230?

No! The 7230 uses a mini USB connector.
The 7730 has a charger in the cradle/base and is different than the 7200 series.

Thanks.

Does that mean that I need to take the cradle with me when travelling for charging?

No, there is a cable included for travelling -- the old 7750 I had had a cable that was big USB on one side (for charger or PC) and BB serial port on the other. I lost like 6 of these (travel a lot and always seem to be a day late ;) ) and they cost like $50! Be careful with yours...

Should I buy new or new with warranty?

1000 Hkd = 128.67 Usd
2000 Hkd = 257.297 Usd
3500 Hkd = 450.269 Usd

Typically yes, but there is a cable available that will let you synch w/o the cradle.

Should I buy new or new with warranty?

i would alway buy the warranty but thats just me

Yes, I am tending to that way of thinking too. I would buy used at the drop of a hat if the price was low but in this case the difference is not that great.