Was the chemical test done on blood or urine? That makes a big difference as to how to approach your defense. Most lawyers thing if there is a drug result there is no defense. That is an incorrect assumption. There are many scientific and legal defenses to DUI drug cases. You need to find a lawyer who specializes in DUI defense who knows the science and not an attorney who is skilled only in pleading clients guilty.
Make bigger payments and ask for an extension. You need to do all you can to pay this off including borrowing money. If your ARD is revoked you start atcsquare one and all ARD costs that were paid are usually gone.
You may also ask for judge to waive ARD costs on the case that you owe 3000 on and have all money go to restitution.