I have two 512 parcels and want to buy a further 1536 ...

[valerie Inshan]

All the mainland fees are shown here (there is also a link on this page about private regions):

http://secondlife.com/land/pricing.php

[valerie Inshan]

All the mainland fees are shown here (there is also a link on this page about private regions):

http://secondlife.com/land/pricing.php

[Ceera Murakami]

That would be 2048 M2 that you pay tier on, plus your free 512 m2, so you would be paying $15 USD per month tier - an increase of $10 per month.

If you buy just a little more than 1536 additional land, you'll push into the next tier level and be paying $25 USD a month.

[Chic Aeon]

Also for anyone else reading this, you ALWAYS get a message when beginning the buying cycle that tells you how much your tier will increase. If you are not happy with that number, you can just quit the purchase process.