I know that this is not what you want to hear, but no one is going to supply a chart comparing prices between all the various systems.
We can offer advice, but in the end you will have to do some homework on your own.
Quick scan of amigakit.com a few moments ago .... (prices will vary)
AmigaOS 4.0 (Classic Version) = 76.71 euro
AmigaOS 4.1 (AmigaOne Version) = 120.22 euro
AmigaOS 4.1 (Pegasos II Version) = 135.71 euro
AmigaOS 4.1 (SAM440ep Version) = 134.54 euro
SAM440ep (667Mhz CPU) = 584.99 euro
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Take SAM440 for example ...
SAM440ep + AmigaOS4.1 = 719.53 euro + shipping
This price includes the motherboard, RAM and Radeon M9 module but does not include a case, power supply, hard drive, DVD/CD-ROM drive, keyboard, mouse and monitor.
Some dealers offer complete systems for SAM440. Prices vary according to what is included in the system.
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Regarding older systems (AmigaOne, MicroA1, Pegasos II, Amiga Classic):
The official AmigaOne and MicroA1 consisted of a motherboard with CPU module, RAM memory module and AmigaOS 4.0 Developer Pre-release CD. Some of us purchased one of these bundles and built our own systems and some of us purchased a complete system from the Amiga dealer with case, power supply, etc. Some people may be willing to sell their entire system. Price will vary according to what is included in the package.
Although I do not know for sure, I would imagine that the original Pegasos II system included the motherboard, cpu module, memory module and MorphOS on CD. Some people may be willing to sell their entire system. Again price will vary according to what is included in the package.
AmigaOS 4.0 (Classic Version) is available for Amiga 1200 equipped with BlizzardPPC expansion board and Amiga 3000(T) equipped with CyberstormPPC expansion board and 4000(T) equipped with CyberstormPPC expansion board. Again price for used hardware will vary significantly as you gather together the basic system and expansion cards.
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Lastly, I just wanted to let you know that I build my current system 4 years ago (MicroA1/AmigaOS4). I use my system every day and have gone through many OS4 updates as they became available. I purchased AmigaOS 4.1 in September 2008.
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redfox