"plunk down" is correct and usable in written English.
The phrase is often used to mean to place something down in a heavy or careless fashion. For example, "The cat plunked down its toy on the sofa."
For one thing, ordinary players plunk down recognizable words.
They were willing to plunk down top dollar months ahead of delivery of the computers.
In fact they were willing to plunk down $12 or so to basically watch him give a slide show.
"Moviegoers don't plunk down $8 or $10 to get hammered by ads".
If I were a rich man, I'd plunk down the cash to see this show.
Parents generally do the buying but teenagers occasionally plunk down allowance or baby-sitting money.
Locals seem happy to plunk down on the street-level sofa and read the paper.
Just to plunk down a few notes here and there was so much effort.
"I'm willing to plunk down $100 to lie here for an hour".
Usually people have to plunk down two or three hundred bucks to buy a new video game console.
His passion and charisma have persuaded enough of them to plunk down more than $250 million at horse auctions.
