Yes it stinks. BASH amplifiers are known to not last as long as traditional amplifiers. I guess that's to be expected when the components are being vibrated while in use.
1. I would make sure I have at least the same if not greater output in the replacement amp. Without the same or greater wattage it's likely not going to sound as good when pushed.
2. If it's not a plug and play replacement or very close to it, it doesn't matter how inexpensive it is. I don't want to spend my time enlarging holes or making a adapter.
3. $100 over five years is $20/year. Not a huge amount of money in the grand scheme of things.
4. Have you considered trying to repair the amplifier you have? These amplifiers often have the same component(s) that fail over and over. If you are handy with a soldering iron you might be able use the web to describe your symptoms, find out what is likely bad, order up replacement parts and see if that fixes the problem. My guess is that is that shipping will cost as much as the parts themselves...so if it doesn't work you'll be out $20ish bucks.