I definitely agree with the idea of saving a little more to get a little more. Every bike brings its own compromises, so buying fewer compromises and more benefits makes sense---or, budgeting for replacement after purchase (which, as @
Thomas15 notes, can get expensive---manufacturers get really cheap pats, consumers don't.)
You might have that bike for ten or 20 years, and if it is a commuter, might ride it twice a day, ten times per week, for 45 or more weeks each year---that is a lot of time and miles to amortize out the added cost.
As for "The extras money is wasted," that might work for some. Some of us have used cheap parts and better parts and can tell the difference. Either approach is valid, but anyone who has put better wheels on a bike knows that is a difference you can feel. For suspension, the better stuff simply works better---absorbing more impact with less effect on the ride and rider. So sure, you can just tolerate the bigger bumps and use more technique but you will not be as fast as you would be on a bike which helped out more----not that being fast trumps having fun, at least in my book.
But still .... if I were commuting and were going to hang and overweight bouncy fork on the front of my frame .... i would want it to suck up Every bump, and almost be invisible because it was so supple. And, as @
63rickert notes, cheap suspension usually has a short life.
I road from LA to Washington DC on a few bikes, most of it on a $500 Dawes. I commuted for years on bikes I pulled out of the trash and rebuilt. I used friction shifting exclusively up until the very late '80s .... and when I finally broke down and bought a couple of slightly pricier bikes, the difference was enormous. I had a lo more fun riding---even just riding to work---when everything worked and worked well, all the time. back in the day you could leave the front shifter as friction and the back as index (early SIS--not front trim) and I Really appreciated the ability to shift much more quickly and with greater accuracy and less thought to technique---it left me free to concentrate on managing traffic or clearing obstacles, depending on where I was riding.
So, yeah ... the OP Could spend a few months picking through dumpsters and visiting yards sales to collect enough pieces to build up a couple commuters which will marginally get the job done---and save a lot of money. Or the OP could do a lot of test rides, find the Right machine for his/her needs, and buy that.
In my experience, just the added reliabilty of a bike you have had since new and maintained regularly is a huge leap forward from riding bikes others have abused and you have tried to repair, and stronger wheels and better brakes are a huge plus when commuting.