Here in the UK, you'd be hard pushed to get an analogue oscilloscope for that.
$100 is about £60 - you can certainly get a used analogue 'scope for that although getting much over 50MHz bandwidth might be challenging.
Scope prices at radio rallies are generally much better than ebay.
There are no good digital 'scopes for that, perhaps a Hantek USB 'scope?
I don't think there are
any new DSO's except the various USB ones and toy "pocket sized" ones which can be had for $100.
At that price pickings are likely to be slim so the best used DSO at that price will be the once you can actually get hold of. That said they can and do appear and sell on ebay UK for that sort of money - eg see
this listing for a Gould 1602.
For less than $100 you are likely to be looking at one of the early DSO's - these usually offer pretty low sample rates and where they have higher bandwidth they will only offer "equivalent time sampling". Sometimes this generation of oscilloscopes had both analogue and digital functionality (which can be useful).
However you need to be aware that digital oscilloscopes of this age are likely to be irreparable if they break. Some failures might be fixable, especially problems with dried out electrolytic caps, however to get even the sampling rates that they do offer out of the technology of the day some resorted to tricks such as fast CCD devices coupled to relatively slow ADC's and memory or had quite cutting edge custom ADCs built out of, by today's standards, odd logic families such as ECL.
If these custom chips die there are no replacements. Also few of these 'scopes had schematics available.
You might get a tek 468, or one of the 22xx series digitals, or a Gould. You will be very lucky to get anything more modern.