Money can be a very uncomfortable subject. And with weddings, there is a LOT of money things. Most people know the rule of thumb that your gift should equal the cost of your meal. But...how much does your meal cost? I have a short answer and a long answer for you because - like with most wedding things - it's a little complicated.
The Short: $100-$150 per person
The average American wedding costs $35,000 (nation-wide, being the key. New York weddings average over $60k!) The average number of guests at weddings is 120. 50% of your budget goes to your reception, so that means $150/per person for the cost of the reception. This will also include things like cake, reception hall, open bar, tables, chairs, and any other miscellaneous thing the venue finds to charge you, so the meal itself probably costs closer to $100. Gage the wedding - is it's really big in a super fancy ball room? $150 might be the way to go. Is it an average wedding? $100 should be fine. But remember: this is per person. If you get a plus one, than your gift should be double.
The Long: What can you afford and what does the couple need?
I had a friend who came in from out of town for my wedding. She had to get to the wedding, pay for a hotel, and take off work (she works retail while going to school). So when she gave us a $20 wedding gift I didn't bat an eye. I completely understood that attending my wedding was (somewhat) a financial burden. Then there was the family friend who was successful, owned his own business, and brought a date. We only got $100 total from him and his plus-one. This annoyed me.
Maybe the bride and groom are paying for the wedding themselves (like my husband and I) and could really use the money to replenish their savings. Maybe you can afford to give a little extra. If this is the case, then bump up your wedding gift. There will be people at the wedding that can't afford the average.
Maybe the bride or groom's parents are paying for the whole thing. Maybe there's 300 people, and you're still not sure how you made it onto the list. I would say it's okay to give a little less this time.
What about the Bridal Shower?
The shower gift does NOT count towards your wedding gift "quota." Not everyone gets invited to the shower, first of all. And if you really can't afford both a shower gift and a wedding gift, it's completely fine to decline going to shower (but if you go, you need to bring a gift). $50-$75 is the typical bridal shower gift - and that cost is per couple (not per person).