Please note this has been updated: 6/14/13. I found that I poorly translated some things and they weren’t completely correct, (see Garden shop) but having actually played the game, I now understand what they meant.
Tent: Pay 10,000 bells
House (4x4 Main Room): Pay 39,000 bells.
upgrade to 6x6 Main Room: 98,800 bells
upgrade to 8x8 Main Room: 198,000 bells
4x4 Second Floor: Pay 289,000 bells
upgrade to 6x6 second floor: 498,000 bells
upgrade to 8x8 second floor: 598,000 bells
4x4 Additional Rooms (left right, & back wall): Pay 348,000 bells
upgrade to 6x6 additional room: 498,000 bells
upgrade to 8x8 additional room: 598,000 bells
4x4 Basement: Pay 428,000 bells
upgrade to 6x6 basement: 498,000 bells
upgrade to 8x8 basement: 598,000 bells
[ The total cost to fully expand your house: 7,595,800 bells. ]
T&T Mart: Play for 7 days, upgrade tent to house, spend 12,000 bells / buy 15 items
Super T&T Mart: 10 days after you upgraded to T&T mart, 10 days after opening the Garden Store, and after spending 25,000+ bells.
Home Center: 21 days after you upgraded to Super T&T, spend 50,000+ bells
T&T Emporium: 30 days after you upgraded to Home Center, unlock Gracie, spend 100,000+ bells.
Cyrus: Play the game for 7 days, have 50+ pieces of furniture and 10+ pieces of clothing in your catalog, make 100,000+ bells by selling to Reese at Re-Tail.
Kicks: play for 10 days, spend 8,000+ bells at Able Sisters
Shampoodle: 7 days after Kicks has opened, spend 10,000+ bells at Kicks/Able sisters
Sable (for QRCodes): befriend her by speaking to her everyday for 16 days straight.
Gracie Grace: Spend 70,000+ bells at the Home Center. She will then appear by the town tree. She must approve of your fashion sense (to do this you must have your entire outfit matching) 4 times. Her store will not open until you have unlocked the T&T Emporium where it will be on the 3rd floor.
Garden Center: 5 days of playing, interact with at least 30 Plant items. Do any of the following actions: pulled weeds, watered flowers, planted trees or flowers. If you don’t have a watering can, speak with Isabelle at her front desk in the town hall and ask for advice. If you do all of the things she asks, she will eventually give you a watering can.
House of Fortune: Have Katrina tell you 20 fortunes
Club lol: Unlock Super T&T Mart, 5 days after Shrunk asks you to gather signatures.
Museum Second Floor: donate 20 items (note it must be 1 of each category: at least 1 fish, 1 bug, 1 fossil, etc). Once that has been done talk to Blathers when he is awake (evening).
Brewster Café: 7 days after you have upgraded the museum, donate 50 items to the museum.
Happy Home Showcase: Speak to Digby who will appear in your town on the second or third day of playing.
Dream Mansion: Speak to Isabelle 7 days after becoming mayor. It will be a Community Project and will cost 234,000 bells. You turn the money into Lloid at the train station.
Reset Surveillance Center: Quit without saving. It will show up as a Community Project costing 368,000 bells
Police Station: Talk to villagers until one request it. Will Show up as a Community Project costing 264,000 bells. You can choose from a Modern style (Copper), or a Classic style (Booker).
The Island: Have upgraded your house at least once, wait 2-3 days until Tortimer appears. The next day you will be able to travel to the island for 1,000 bells
Shovel: 500 bells at Nookling Junction
Fishing Rod: 500 bells at Nookling Junction
Net: 500 bells at Nookling Junction
Axe: 400 bells at Garden Shop
Watering Can: 500 bells at Garden Shop
Sling Shot: 500 bells at T&T Mart
Timer: 500 bells at T&T Mart
Megaphone: 500 bells at T&T Mart
Hammer: 10 medals from Island store
Silver Shovel: 500 bells at the Museum store after paying off the Community Project
Silver Fishing Rod: 500 bells at the Museum store after paying off the Community Project
Silver Net: 500 bells at the Museum store after paying off the Community Project
Silver Axe: 8 medals from the island store
Silver Watering can: Buy 50 flower bags from the garden shop
Silver Sling shot: Shoot down a silver balloon.
Gold Shovel: Buy 50 bags of fertilizer from the garden store
Gold Fishing Rod: Catch all fish and speak to Chip during the fishing tourney
Gold Net: Catch all bugs and talk to Nat during the bug catching tournament
Gold Axe: Buy 50 seedlings from the garden store
Gold Watering Can: Maintain a perfect town for 15 straight days and talk to Isabelle
Golden Slingshot: Shoot down a golden balloon.
Diving Suit: Unlock the Island. It will cost 40 medals at the island shop
Mannequins: Unlock Sable. purchase 51 pieces of clothing from Mable, purchase 31 accessories from Lablle, and you’ll receive it from Gracie when she is unlocked.
[ I hope this is helpful for some of you. If you have any questions please feel free to ask! ]
[ I want to thank Nookipedia and my copy of Tobidase Doubutsu no mori strategy guide to help me compile all this information! ]