I have not seen an inexpensive one (such as the ones for around 100.00 used in the automotive ind) that will fit down a bore much smaller than a shotgun.
That being said i purchased an old ACMI borescope on ebay for around 40.00. ACMI was purchased by Olympus and are commonly used in the medical industry. The clarity is excellent. The down side is that the light source is antiquated and the last bulb burned out and they are no longer available. I am currently in the process of retro-ing an LED light.
Basically keep your eye on ebay for good prices on used medical borscopes, or cystocopes (same thing just used in the uriology field) or spend 800+ on a hawkeye.