Since almost ALL amps use the exact same or similar parts, the difference is not in the parts, it's in the quality of the PCB, the capacitors used, and the customer service of the company you are buying from. If you purchased a $4000 amp but couldn't get any help with it when you have problems does that still make it a good amp? I don't know, I would guess you would be throwing it away or sending it to a repair shop to pay for it out of your own pocket... Doesn't sound like a "good" amp to me....
For a beginner, without a lot of $$$ to spend, try the HiFonics line, not too bad and if you shop around you can get them VERY cheap, but beware, as many places that sell these amps cheap are not authorized to sell them and Maxxsonics (the parent company of HiFonics and many other amps) will not warranty your amp.
And DON'T mount it to the speaker box... bad idea, will shake it to pieces over time. I know because I work on these things everyday.......