that is based off the prices i see on my FB groups, ebay might be a different story, i would check "sold" listings and what a lightly used 3.3 goes for.
probably get around 50-100$ each, nitro engines are a hard sell because of so many factors being the break in used, how well it was broken in, how much actual life they have on them, and how much life was used, what fuel etc. buying a used nitro engine is really just a complete guess and...