Perhaps it is just an infection - and at any rate plenty of colloidal silver and echinacea can't hurt and may well help. Note though that if you suspect tetanus or have symptoms which persist or worsen, it is always advisable to get a professional diagnosis imo.
Actually the price of the product you mentioned is more like $25 a bottle. However, the company has a first time buyers special where you can buy one and get one free for up to three bottles (six total for the price of three plus shipping), sometimes has sales up to 50% off (as might still be the case with their last sale) and the price per ounce is much reduced when you opt for the gallons or 5 gallon sizes - especially when you find them on sale.