Weddings can come with a lot of big expenses. The Knot's 2015 real weddings study found that the national average cost for a wedding was $32,641, and that number can be much higher in certain areas of the country.

Weddings usually aren't cheap, and vendors often take advantage of customers by marking up services intended for weddings.

Usually, soon-to-be newlyweds are aware of the annoyingly high costs for alcohol, gratuity and floral necessities. But there are a lot of unforeseen costs that have nothing to do with tulip arrangements or open bars that may sneak up on you before the big day.

1. Cleaning services at the venue.

If you don't have a traditional catering or staffing company managing the food at your wedding, you may not be guaranteed any clean-up services at the end of the night. This may mean hiring someone (or a group of people) to serve as a final clean-up crew so you don't get fined for not properly cleaning up the venue. The level of cleanliness required depends on the type of venue and its rules.

"For wedding clean up, it’s important to pay attention to the rules at your venue — some just want all of your personal stuff out, some expect all furniture to be broken down and the floors to be both swept and mopped, most are somewhere in between," wedding planner Elizabeth Clayton advises in the blog A Practical Wedding.

The Knot also notes that venues only providing space may charge up to $500 for garbage removal and final clean-up costs.

2. Bridal dress contracts.

Flickr/Annie - flickr.com

Brides may be required to sign bridal contracts while purchasing their wedding dress, and this could mean taking on unexpected alteration costs. Writer E.J. Dickson wrote in a July piece for The New York Times that she signed a bridal contract when buying her dress, but that she became pregnant a few months before her wedding and faced the reality that her dress might not fit perfectly, or at all.

"When I get married Aug. 27, I’ll be about four months pregnant. I won’t exactly look like the Hulk — maybe more like Superman after having a few Chipotle burritos — but it’s possible that I’ll require alterations nonetheless. And as per my contract, if I do, I’ll bear full financial responsibility for them," she wrote.

You may not have a pregnancy right before getting married, but if you lose or gain weight prior to your wedding, alteration costs might be necessary, and alterations can cost hundreds of dollars. This cost usually doesn't include the amount that you spend on a dress when you buy it, or the accompanying jewelry and veil.

3. Feeding vendors.

Certain vendors require clients to provide them with a meal, particularly if they are working the entire wedding (i.e. photographers, videographers, wedding planners). Though you might not want to feed anyone who isn't a guest, Brides.com writer Heather Lee insisted in a 2014 piece that you don't want a tired, hungry vendor on what might be the biggest day of your life.

"[T]he last thing you want on your wedding day is a low-energy DJ or an exhausted photographer. Your vendors are putting on your affair so that you don't have to, so plan on feeding any wedding professionals who will be there with you at the reception," Lee explained.

On average, wedding catering costs come out to around $85 per person, so if you're feeding your vendors the same food that you're giving to guests, you could end up spending a lot more money than you anticipated. To keep costs low, some people provide boxed meals for vendors rather than the catering food that they serve guests.

4. Hair and makeup trials.

Some brides like to do hair and makeup trials before deciding on a makeup artist and stylist for the big day. This enables the bride and stylists to get to know each other, and to see what looks work and do not work prior to the wedding. But these trials aren't free.

Lindsay Goldenberg Jones, the founder of wedding site Woman Getting Married, wrote in a 2010 post that hair and makeup trial runs can cost "anywhere from $50-$150." In addition to paying for day-of hair and makeup costs, brides may also be expected to pay travel and parking fees for stylists.

"I think $65 for hair/makeup trial is a fair price to be argued for," Jones wrote. "You can also expect to pay for their travel, which typically runs you $30 depending on location, plus the cost of valet."

5. Wedding invitation postage.

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Don't automatically assume that your wedding invitations only need a standard $0.47 stamp each. These invitations might weigh more than you think and will probably require additional postage, especially, if you're including RSVP cards, envelopes and other additional materials.

"Before you mail your wedding invitations, ask the post office to weigh a fully assembled envelope so you know exactly how many stamps you'll need," The Knot's Amanda Black advises. "This step may sound tedious, but the alternative could mean invites returned for insufficient postage, which will throw your entire wedding planning timeline for a loop. Enclosures typically increase postage, so keep that in mind when you're deciding on inserts like maps or reception cards."

Whether you decide to have a massive Kardashian-style wedding, a backyard get-together, or a simple nuptials ceremony at the courthouse, hopefully these tips will help you avoid going over budget and adding unnecessary stresses to your big day.