Options:
a) Get a real Amiga 2nd hand.
Slow, old, buggy, hardto repair and costs a fortune ....
b) Install UAE (the Windows-version is the best). It's a complete emulator that
will run anything from old games to power-apps (those will often be faster than on
any real Amiga).
You would still need an AmigaOS for that, and if you don't have that, you could buy
AmigaForever from cloanto, which is UAE bundled with AOS3.1 ready to start.
UAE itself is free and opensource.
b) Get a copy of Amithlon (sold in the AmigaOS-XL-package), probraly the fastes
"Amiga" forever (since it runs on the fastest x86-CPU). This will require a PC with
a limited choice of GFX/net/sound-cards,is somewhat harder to setup. It does not
need a full OS underneath as it is based on a hacked-into-place linux-kernel.
It also comes with AmigaOS3.9 and some basic apps.
Downside is that it is entangled into some ugly infighting between those
who conrtibuted to it,which makes further development unlikely. It will
only run "clean" 68k-Amiga-apps which don't do any direct HW-accesses.
c) Pegasos/MorphOS will run all that Amithlon runs, plus 68k+PPC-SW and
some native pure PPC_SW. The orginal Pegasos1 has been discontinued due to
probs with the Northbridge(vendor), and the 2nd revision has just reached
(pre)production, featuring Gigabit Ethernet and DDR-RAM. These will cost
299 for a G3/600 and 499 for a G4/1000.
The Peg1 with G3/600 is (in my experience) faster than Amithlon on an AthlonXP1600,
which is mostly due to the PPC being better suited for 68k-emu,and the fact that the
Pegs run MorphOS instead of an emulated 68k-copy of AOS.
MorphOS is a 100% PPC-native reimplementation of AmigaOS3.1,pluse
the most important features of 3.5/9 and some MorphOS-specific extension.
It is all you could expect from an Amiga, except for the name.
d) AROS, a reimplementation of AmigaOS3.1, without support for any old SW,
still lacking some importantfeatures,but completly free and opensource. It does
(in theory) run on all kinds of CPUs, but the most advanced versions are
the native x86 and the x86-linux-hosted.
e)AmigaOne/OS4, the "official" solution, costs even more than a) :-o , isn't
available (no release-date set) and well .....
(maybe I'm not the perfect choice to explain that option :-D )