I don't think $100 for a chef's knife is antimustachian. I recognize that it could be a large purchase for you, but good knives are worth their price if you cook. They hold up very well and make it more enjoyable to prep. I don't take good care of my things so I'm content with my relatively cheap knife set, but I plan to buy a good chef's knife one of these days.
Yup, I bought an $80 chef's knife about 6 years ago, along with a sharpening stone setup. I still use it to this day and sharpen it every 1-3 months. I've had my eye on a $100 one from a popular online vendor, but just can't justify it since my current one works so well.
For those of you who claim to have had a knife over 6 months without sharpening that's still sharp, color me skeptical. I suspect you just haven't used an actually sharp knife in a long time. Dulling is one of those things that happens so gradually it's tough to tell if you aren't looking for it. That's why every review online for any knife talks about how sharp it is, the reviewer is transitioning over from their old knife.
Is your 3 year old knife sharp enough to work? Yeah, I've used knives at other people's houses that were brutally dull, but they still do work as long as they're some sort of thinnish metal wedge. You typically have to put what I consider a dangerous amount of force behind the cuts, but you can get the job done. My recommendation is get a $30 king combo stone and learn how to sharpen by hand. It's got a bit of a learning curve, but it's a good skill to have. That $30 stone will probably last your whole lifetime, and will save you a few knife purchases over the years. It'll also make your brisket slices nicer, and your homemade sushi cleaner.
edit: A great example is my girlfriend's aunt. She's had the same old knives for probably ten or more years, and my girlfriend's grandma insists she only likes these old knives and they're just right for her and are plenty sharp. I finally got them a Victorinox 8" because I didn't always remember to bring my knife when I planned on cooking, and basically massacred a huge brisket that took 15 hours to cook. Once they got the Victorinox, grandma quickly changed her tone and loves it. They both couldn't believe how sharp it was and how easy it cut through everything.