The most expensive items in Habbo only exist in incredibly small quantities (mostly in single figures). There are not many items that still can justify a price reaching into the thousands, even fewer can still command a value higher than the maximum market price of 10,100 credits.
The most valuable items are undoubtably the unique items due to their sheer exclusivity. The most well known of which are the
Executive Ice Cream Maker,
Childline Rug,
Quick Coffee Stop,
Watering Can of Greatness! and more currently the
Purple Monolith (Spaceship door). The Executive ICM last sold for around 500gb (25,000c) post-casinos and the Watering Can 200gb (10,000c) last month.
Straypixel Easels also carry a high value, they come in 5 forms: Winners
x1,
x3 (14 existing),
x5 (7 existing),
x7 (4 existing) and
x10 (only 2 existing). Because of their extreme rarity not even Habbox Rare Values has a figure for x5, x7 and x10 because they aren't traded. The Straypixel x3 has been sold for up to 140gb (7,000c) recently so I can imagine the rarer ones would fetch a higher price. I believe one of the x10 has been permed (I think) on :ashez: (along with some other easels) and the other x10 has been lost - so perhaps this would be a strong contender for the most valuable item if the other one turned up in circulation. I don't think the Art Easel is in circulation, with the only example existing in
NotMiceElf's Straypixel Help Desk (Staff).
However just because an item is rare it doesn't necessarily mean it is ridiculously expensive. For example the
Arcane Rares, which consists of the
Amber Floor Rug,
Army Plasto Chair,
poster_0_name and the
Zon Parasol. These items exist in small numbers and look similar (or identical) to other normal furniture, however are not too expensive.