Advice on repossession after serving section 21 notice

I am private landlord and used openrent for contract with a tenant who gets DSS help from council. After serving the section 21 notice, tenant is happy to move but council wants then to move only after bailiff order is given as they want to buy more time.
The notice will be over end of February. I checked with a few solicitors to help me complete N5B and then if required apply for bailiff order. The range of cost was £2000-£3500. Is this the usual cost or I can get it done cheaper or do myself? I wanted to get them involved so that legally it is all good and I get repossession. Please help.

You can do it yourself. The landlord associations have detailed guidance on making a possession claim and telephone helplines if you get stuck.

Thank you. Do you have a link to it please?

In England the main options are Tessa Sheperson or the National Residential Landlords Association. You can google them and then ask if they have what you want before joining.