You would pay VAT on 100,000 leva, which is 20,000 leva. As in the UK you are either registered for VAT or you are not, which means either you have nothing to pay or you pay on the full amount of your sales in any tax year. Quite sure that the buyer wouldn't want the full price put on the notary deed, though, as it would mean they would pay more in notary fees on their purchase.
I have never met anyone who has closed their company; when it became possible to hold property in your own name I got two or three quotes for closing my company. All were around 600euro, which seemed an awful lot as I had closed a company in the UK before coming to live in Bulgaria and the cost was only £10. As my accountant only charges 50 leva for a nil return I decided to stick with the company until prices were a little more sensible.
The alternative to closing a company is to sell it as a ready-formed company (just as you can buy off-the-shelf companies in the UK) then all that is needed is to submit forms to change names on the company formation documents. Ask your accountant or a lawyer if they know anyone who wants to buy a ready-made company, but also check what they would charge to transfer it to a new owner. Again, the necessary forms will be downloadable from brra.bg