Here's a complete bash script that accomplishes the tasks you've outlined:

#!/bin/bash

# Prompt user for directory path
echo "Enter directory path:"
read dir_path

# Prompt user for number of columns
echo "Enter number of columns:"
read cols

# Prompt user for number of rows
echo "Enter number of rows:"
read rows

# Calculate total number of images and total width
total_images=$(ls -1 "$dir_path"/* | wc -l)
total_width=$((cols * 230)) # 200px for each image plus 30px gap

# Check if total width is greater than 300px, if so, increase rows
if (( $(($total_width / 300)) < $rows )); then
    rows=$(($total_images / $cols))
    if (( $(($total_images % $cols)) != 0 )); then
        rows=$(($rows + 1))
    fi
fi

# Calculate total height
total_height=$((rows * 300))

# Prompt user for output file path
echo "Enter output file path:"
read output_file

# Create contact sheet using Montage
montage -geometry +0+0 -label "%t" -pointsize 20 -background white \
        $(ls -1 "$dir_path"/* | sed '1d' | awk "NR==$total_images{print}") \
        -tile "$colsx$rows" -geometry 200x300\> \
        "$output_file"

echo "Contact sheet created successfully!"

Save the script as a file (e.g., contact_sheet.sh), make it executable (chmod +x contact_sheet.sh), and run it (./contact_sheet.sh). It will prompt you for the necessary inputs and create the contact sheet file in the specified output path.