You need to have the governing documents of the HOA and the documents imposing the special assessment examined by an attorney. Do NOT let this go to sale on the lien. While you do have a 90 day right to redeem following the sale, it will only become more expensive as time passes.
This answer does not constitue legal advice, nor does it creat an attorney/client relationship. If you are seeking legal advice upon which you intend to rely, you should hire competent cousel familiar with this area of the law in your locale.
Just as an addition, have you looked into bankruptcy as an option. It is difficult to determine from the facts of your case but you may be able to avoid the HOA lien in Chapter 13 bankruptcy case. Whether this is beneficial in your case depends on evaluation your overall situation and other debts.