Hi J.,
In my experience, this is a situation that can be fixed, but it takes time. My daughter was the same way, potty trained completely during the day and soaked at night. I realized that I created the need for the night time pull up. As she was learning to potty train during the day, she would become devastated at night if she wet the bed. So in my efforts to help her not be discouraged about her day time training, I put her in pull ups at night. This was a fix at the time but not a long term solution. By age 4, I decided that the pull ups at night needed to go, they were expensive and I knew that she could now handle this responsibility. It was a struggle but well worth it. First I got several mattress protectors, not those little pad things that go under their bottom, the kind that protect the entire mattress no matter where she rolls durning the night. I started by limiting her beverage intake at least an hour before bed and eliminating the pull up. After she went to sleep, I would wake her every two hours to use the potty until I went to bed. Gradually the waking times got further and further apart until, I did not wake her at all. She did have many accident but she also learned how to wake up on her own to go potty. My daughter was and is still a very sound sleeper, but she no longer wets the bed. The entire process did not take long, it just caused a lot of laundry, but it worked well for us. I guess you just have to weigh the options, extra laundry for a few weeks or keep buying pulls up for the next several years.
What ever you choose, I wish you luck