And she hasn't even been invited to the wedding itself, or even the evening do.
"She's driving 3.5 hrs on Friday evening, taking two people. Paying £160 for 2 nights at a hotel. Couldn't get the Friday off work and told the group this - but they've arranged it so that the (paid for with her hotel money) events -spa day etc are all in the day on Friday," reads the post.
"It's being demanded she pay £50 towards a table in a club (which is 1 hr from where they're staying). And food and drink isn't included. She's then driving 3 people back on Sunday."
It's not even the bride that's demanded this, says the poster.
"The organisers have taken it upon themselves to plan what the bride doesn't want, insist on paying for her (when possibly her reason for this is because she knows there's at least one guest attending who won't be attending the wedding) and have left out 3 guests at least in their plans," she says.
Mumsnet users are divided between those that think it's outrageous exploitation - and those that think the put-upon guest is simply a walkover.
"Inviting someone to spend a bunch of money like that when they aren't invited to the wedding is extremely poor etiquette," says one.
"Knowing she can't make the Friday and arranging the spa etc. on the Friday is just nasty. Do these people even like her at all?"
But another comments: "She's being treated like an utter doormat and she's allowing it!"
While the rising cost of weddings is frequently highlighted, there's less sympathy for the plight of guests. But in a recent report from market research firm Mintel, it's been revealed that the average stag or hen party costs guests £164.
"Hen and stag parties have also become big business, morphing from what was traditionally a night out with friends into fully fledged, multi-day celebrations in their own right," says Jack Duckett, senior consumer lifestyles analyst at Mintel.
"The rising cost of stag and hen parties reflects the increasing breadth of activities groups look to include in their celebration, ranging from afternoon tea and wine tasting experiences to spa weekends abroad."
£20,983 wedding: where the money goes
£20,983 wedding: where the money goes
This is the biggest expense, and accounts for 16% of everything couples spend on the wedding. There are endless dramatic places to splash the cash, and if you want to get married in a castle, on a beach, or in a major historic property, it’s all perfectly possible - for a price.
However, there will be those who wonder why the wedding can’t take place in a church or a smart registry office - and the reception in a village hall. These places certainly exist, and could cut the venue hire cost down to a couple of hundred pounds.
It’s not hard to see why couples fancy blowing a fortune on an incredible holiday, but it begs the question of whether it’s such a practical idea.
There’s no earthly reason why two such enormous costs have to be bunched together like this. Surely a wiser approach would be to get married, and then start saving for a great holiday. You don't have to be on a white beach in the sun for it to be romantic or memorable.
This is a huge sum for feeding a few people, and is often the result of the fact that when you are booking a venue, you will be tied into using their caterer.
It’s one reason why a fantastic way to cut costs is to find a venue that lets you do it yourself. That way you can choose between setting out a cold buffet in the morning on a shoestring, or hiring in a cut-price catering option, like a gourmet burger or pizza van.
This includes the cost of an engagement ring and two wedding rings. There will be couples who argue that this is something that you’ll wear every day for the rest of your life, so is worth investing in.
There will be others who highlight that by shopping around you can get the lot (including the obligatory diamond) for less than £400, and anything else is pure vanity.
This includes a heart-stopping £1,098 for the bride’s dress. Just to be clear, that’s a grand for a dress you wear once.
There are hundreds of second hand dresses on sale on sites like preloved if you’re after the big meringue, or you could get one made from scratch for a couple of hundred pounds. Then if you sell it on again afterwards, your dress could cost you less than 20% of this insane figure.
If you’re stuck buying the overpriced booze offered by a posh venue, you’ll easily bust the budget, and if you bring your own to a venue like this they’ll sting you for corkage instead.
A much better idea is to find somewhere that lets you bring your own - and after the first few drinks, ask a local pub to run a bar for you.
The argument in favour of spending a fortune on photos is that this is one aspect of the day that really will last, and if you skimp on the photographer, you won't have a beautiful album to linger over for decades to come.
That said, you'll probably have one hour of looking at your best during your wedding - from when you walk down the aisle, to the moment you have finished taking the obligatory formal photos. There’s nothing stopping you bringing in a professional for that hour, and then setting up a Facebook page for your friends to post all the photos they take throughout the rest of the day and night.
The live band feels vital for some couples, but ask yourself, when was the last time you were blown away by the live band at a wedding?
A far cheaper option is to make your own disco. It’s easy enough to hire some speakers and lights, switch it all on, plug an MP3 player in, and get your favourite music all night for next to nothing.