Python script to find large folders

I wrote this script a few days ago to find all files which were taking up over a certain threshold of memory on the hard drive. A hard drive on one of my computers had just 6 GB left, so I needed to clean some space up. I used this to identify bulky folders to find out where the problem was.

Is there anything I could have done better? I'm particularly displeased with the exception handling in the get_folder_size function, since I ended up handling the same exception twice, just at different levels. Couldn't think of a way around it off hand, though. Also, efficiency was an issue with this script. I know I could've invented some framework to keep track of all the folders previously scanned, but that seemed like a bit too monumental of an effort to make for such a trivial script. The recursion was much easier to implement.

Any and all suggestions are welcome!

import os

BYTES_IN_GIGABYTE = 1073741824
GIGABYTE_DISPLAY_LIMIT = 2
ACCESS_ERROR_CODE = 13

def get_folder_size(filepath):
    size = os.path.getsize(filepath)
    try:
        for item in os.listdir(filepath):
            item_path = os.path.join(filepath, item)
            try:
                if os.path.isfile(item_path):
                    size += os.path.getsize(item_path)
                elif os.path.isdir(item_path):
                    size += get_folder_size(item_path)
            except OSError as err:
                if err.errno == ACCESS_ERROR_CODE:
                    print('Unable to access ' + item_path)
                    continue
                else:
                    raise
    except OSError as err:
        if err.errno != ACCESS_ERROR_CODE:
            raise
        else:
            print('Unable to access ' + filepath)
    return size

def get_all_folder_sizes(root_filepath):
    folders = []
    for item in os.walk(root_filepath):
        if os.path.isdir(os.path.join(root_filepath, item[0])):
            folders.append([item[0], get_folder_size(item[0])])
    return folders

def convert_bytes_to_gigabytes(bytes):
    return bytes / BYTES_IN_GIGABYTE

def main():
    folder_sizes = get_all_folder_sizes('C:\\')
    folder_sizes.sort()
    for folder in folder_sizes:
        gigabytes = convert_bytes_to_gigabytes(folder[1])
        if gigabytes > GIGABYTE_DISPLAY_LIMIT:
            print(folder[0] + ' = ' + format(gigabytes, '.2f') + ' GB')

if __name__ == '__main__':
    main()