Apple 27" iMac MC813LL/A [Mid 2011] Quad Core 2.7GHz CORE i5 2500S 8GB 256GB SSD

This computer costs about $600.00 (check prices)

Maximum RAM: about $100 for 16GB

Hard Drive Upgrade: Not needed really unless you need more space. I would be fine with this size.

It’s quite possible you could buy this iMac for about $600 and then just use it. If you needed  more ram you could add 16GB for $100 so about $600 or so would get you a very nice iMac with a fast i5 processor and enough ram and a fast SSD already installed

APPLE A1347 MC270LL/A Mac mini 4.1 Core 2 Duo 2.40Ghz 4GB 320GB - HDMI

This 2010 Apple Mac Mini (see full specs) tend to sell now for about $200 to $250.00  which is a pretty good price for the last mac mini you can use with an internal disk drive.

This particular model ships with 4GB of RAM which you can double to 8GB for about $50.00

The hard drive is an okay size at 320GB but you could add a 250GB SSD drive for about $100.00 to make this mac mini much faster than if you were to use the standard drive.

Total Upgrade Price for APPLE A1347 MC270LL/A Mac mini 4.1 Core 2 Duo 2.40Ghz 4GB 320GB 

If you add the cost of the Mac Mini and double the RAM ot 8GB and swap out the drive to an SSD drive you should be able to spend less than $400 for a Mac Mini that still has lots of life left.

Apple MacBook Pro 15 A1286 2.53GHz Intel Core 2 Duo 8GB Ram 250GB HDD 10.6.8

This  Apple MacBook Pro 15 A1286 2.53GHz Intel Core 2 Duo 8GB Ram 250GB HDD 10.6.8 tends to sell for about $250.00 now. That’s a pretty good price for a 2009 MacBook Pro with the following specs

It already has the ram maxed out to 8GB which is the maximum ram you can install in the 2009 MacBook Pro Models.

The  only upgrades you would need for this model would be:

Hard Drive

SSD drives make a world of difference in these MacBook Pros and the original drive in this is only 250GB anyway. If you replaced the hard drive with the same sized SSD drive you would not lose any space and yet have a much faster MacBook Pro.

Battery

You will need a new battery. You can buy a 3rd party battery for about $30.00 for this MacBook Pro.

If you swap out the hard drive for a faster ssd and add a new battery to this Mac you can have a very nice MacBook Pro for about $400.00 after upgrades.

Apple MacBook Pro 13.3" LED Intel i5-3210M Core 2.5GHz 4GB 500GB Laptop MD101LLA 

The Apple MacBook Pro 13.3” LED Intel i5-3210M Core 2.5GHz 4GB 500GB Laptop MD101LLA sells for about $600.00

This 2012 non-retina Macbook Pro is a bit on the old side now but it’s still got a lot of life left if you added a few upgrades:

2012 MacBook Pro RAM

This MacBook Pro ships with just 4GB of RAM but it can accept at least double to 8GB with ease for about $50.00

2012 MacBook Pro Drive Upgrades

You have 2 options when it comes to upgrading the 2012 MacBook Pro Hard Drives:

Add a spinning hard drive to at least double the capacity to 1TB of storage if not more. This is a pretty cheap upgrade at about $50.00

Add a SSD Drive. This is much faster than a regular drive and although you don’t get the capacity of the spinner, you do gain a lot of speed making the MacBook Pro much faster. SSD Drives are about $100 for 256GB models and $200 for 500Gb capacity

Other 2012 MacBook Pro Upgrades

As this is an older MacBook Pro you might want to consider a few upgrades other than RAM and storage:

Get a replacement power cord. These cost about $30.00.

Get a new battery. Battery life on a 5 year old computer is bound to be worse than at release time. You’re good to go with a replacement though at about $30.00

Lastly, don’t forget to protect your MacBook Pro from bumps and scratches with a protective sleeve and if you need more screen real estate adding a second monitor is a great way to increase your productivity too.

some resources:

RAM Upgrade Instructions

Hard Drive Upgrade Instructions

Apple MacBook Air 13.3" LED - Intel Core i5 - 8GB RAM - 128GB Storage MMGF2LL/A 

This MacBook Air from 2015 tends to sell for about $1000 (check price)

128GB PCIe-Based Flash Storage. Apple 13.3” MacBook Air MMGF2LL/A. 8GB of 1600 MHz LPDDR3 RAM. 1440 x 900 Native Resolution. 802.11ac Wi-Fi, Bluetooth 4.0. Main Features. 13.3” LED-Backlit Glossy Display.

There’s really not a lot of upgrades you can do for this MacBook Air.

2015 MacBook Air Hard Drive Upgrades

You can upgrade the MacBook Air’s Hard Drive to a larger storage capacity, but it’s not cheap with 256GB SSD Upgrades going for about $250.00 check price and 512GB SSD’s selling for about $350.00 check price

A few other upgrades to consider would be adding a new battery (not sure you need it in a 2015 model) or adding a monitor for more screen real estate.