I would have to disagree with you that Macs are not cheap. For example, I still own Macintosh PowerPC G4 models circa the years 1999 to 2001 that I still use. I was running three operating systems - Classic, Mac OS X, and Windows XP at the same time on these units with drag and drop between all three operating systems - i.e., this was not a scenario where you needed to reboot the Mac into each operating system. I was running TurboLister on XP back then because eBay started to charge money for using their API which meant my previous Mac listing tool was no longer made because the publisher could not afford to pay for access. TurboLister was one of the worst programs ever created - I cringe at ever having to use it.
These Macs cost more than PCs at the time because they were among the first dual processors which were derived from Power Computing Corp. which Apple bought. They allowed you to install four internal hard drives in the standard bays. I still use them to run legacy software and equipment such as old scanners which perform much better than anything they have today other than a professional studio equipment. I've even updated the PATA hard drives to modern SATA hard drives and installed better graphics cards.
You get what you pay for! I've yet to see a modern PC do what these 16 year old machines do.
On my current Mac Pro I am able to run Windows via VirtualBox and some Classic software via SheepShaver although this is also mainly for running legacy software.
This site lists specs for older Macs and sells parts for older Macs.
For the best deal on new Macs I'd stick with one of the larger Mac resellers because they are competing against each other and will offer deals such as a free printer, software, and so forth with a purchase of a new Macintosh. Some will have progmotional giveaways with 3rd parties. For example, I purchased a new Mac Pro system from one of these retailers who gave away a Canon $400 six color printer. I sold the printer on eBay which translated to money off my system.
If you see a drop in prices it likely means a new model is coming out and the resellers are thus trying to get rid of the older models. This is best time to buy. There is no need to buy the latest model since in 3 to 6 months the current new model will be the old model.
I'd be sure to get as much RAM installed as possible! My main computer is a aluminum cased Mac Pro Quad Core with 48GB Ram and multiple hard drives installed as I use it for graphics work in Photoshop & Illustrator. If you are using a semi-pro camera to take pictures for eBay you are likely going to need something with lots of RAM and a faster graphics card if you don't want to wait to long while you open a batch of photos to edit.
I've used the following resellers in the past for complete systems, most of which came with extra bonus items:
I've also used Amazon to buy a Macbook Pro - not a dealer on Amazon, but Amazon itself, although Amazon does not tend to give you any bonus items.
I've purchased some legacy items on eBay, but I don't think I'd ever buy a new system as these dealers are having to pay eBay a fee to sell there and typically don't do the volume to offer the discounts that resellers with their own site offer.
Another technique you should use for any large purchase is to essentially make your credit card company pay for part of your system. Look online for credit card signup bonuses. Some of the better offers might give you a $100 to $250 credit for spending a given amount within 90 days. Other signup bonuses may give you a credit for signing up without a minimum spending amount. Apply for the card, wait 1 or 2 weeks for it to arrive, and place your new system on the card. Pay off the card before the due date to avoid any fees and no longer use it if you'd rather use another card or not use a card at all. You might have to wait 1 or 2 billing cycles (months for the credit to be applied to your account).
I've used this technique to get nearly $2,000 in credits - i.e., free equipment.