Your trade fair budget depends on your overall trade fair objective. You will need to breakdown your budget as per the activities you want at your booth. However, as per the general rule of them, you can take the cost of your exhibit space and multiple it with three to calculate the overall cost estimate. For example, if 10×10 exhibition space costs 2000 Euros, then you are fairly looking at the investment of around 6000 Euros for your exhibition participation. Goes without saying, you will need to consider miscellaneous costs for any unforeseen expense.
For detail budget bifurcation, Read the details here (cluster page)