Under standard Monopoly rules, what is the most amount of money a player can lose in a single turn?

Without rolling doubles and landing on multiple improved properties, the most rent a player would have to pay is $2000- Boardwalk with a hotel.

http://monopoly.wikia.com/wiki/Boardwalk

Guessing if many hotels / houses are owned and picked up building repairs card (I can't find exact figures) then the multiple could be higher than 2000

Building repairs are $40 for each house & $115 for each hotel. If you owned all 12 hotels and all 32 houses in the game, the total repair bill would be $2660.

http://entertainment.howstuffworks.com/leisure/brain-games/monopoly1.htm

Well, there is that income tax square to land on. And if some Einstein preferred to pay 10% of his mountain of cash rather than the $200, it may be more than $2000...

I thought building repairs were higher,
Assessed For Street Repairs -- $40 Per House, $115 Per Hotel - sorry.

Can't find my board, but it is possible to land on both Park Lane and Mayfair with a double 1, and they're the most expensive hotels to land on. So what would be the most expensive thing a double throw back from that? Would it be the repairs card or another hotel? If the repairs card is possible, and you had hotels on everything else other than Mayfair and Park Lane, that would give the maximum loss. If that card isn't a double back from Park Lane, then it will have to be one of the green streets with a hotel on it.

If all houses and hotels are out, $40 per house and $115 per hotel is $2660.

Since you go again if you roll doubles and the distance between the dark blue properties is 2, it is possible to land on both dark blue properties with a hotel on a single turn. One is 1500 and the other is 2000, so together those could cost you $3500.

http://www.monopolydocumentary.com/files/Methods_Math_Myths_Handout.pdf

http://monopoly.wikia.com/wiki/Park_Place