Why do you "need" 100+ Mhz?
Because high bandwidth is one of the very few advantages that an inexpensive analog scope has over an inexpensive digital one?
There is no need to go lower, as there are plenty of good 100 MHz + analog scopes out there to be had. At 100 MHz, you will get a respectable 3.5 ns rise time, which is good enough to look at quite fast digital signals, e.g. fast PWM outputs of a micro, fast SPI data/clock streams to/from a SD card or serial flash chip, etc.. You'll also be able to catch high frequency oscillations on analog circuits like amplifiers, power supplies, dummy loads, etc.
I'd suggest:
Certainly don't pay more than pocket change (or equivalent in liquid consumables) for anything less than 50 MHz. You'll outgrow it quickly and will find it difficult to sell for more than pocket change.
Keep your eye on local classifieds like Craigslist etc. JUMP on anything you find.
Look up electronics recyclers in your area and check if any of them test and re-sell working goods that they receive. Where I live (Ontario, Canada) they need a special license to do that, but some do. My best 'scores' have been at such places.