I have to echo much of what has been said here. I use a combination of hardware, a computer, and iOS devices. I finance my music making gear entirely through sales of the vinyl collection I accrued in my late teens and early 20s or from selling other pieces of music equipment so getting the best value from my setup is important.
Hardware:
Secondhand is amazing but a little knowledge also goes a very long way. For example: I get a lot of mileage out of running signals through guitar pedals. I discovered that many of the classic Boss pedals that go for £100-150 were also released as Amdek units which can be found for circa £30. There are countless forgotten gems in guitar pedal world and it’s worth bearing in mind that most of them will have been bought by guitarists whose needs are not the same as synth users. Something that a guitarist hates could be a totally different beast when connected to something that does have strings.
I had a Moogerfooger MF101 that was giving me beautiful Moog tones but at a cost of £300 or so. I discovered that I could modify a Werkstatt which I could get for around £100 to offer more or less the same functionality and now I have that (and the other £200 went on other gear).
Sometimes the right thing to do is to spend the money, though - getting the best value isn’t always buying the cheapest thing. I got a Vermona Retroverb Lancet that cost me more than my MS-20 Mini but it earns that money because it enhances everything I put through it. I too worship at the altar of cheap Yamaha PSS keyboards and my £10 PSS450 sounds like a few hundred £ at least when put through that spring reverb and filter…
Software:
I got most of my software with either my audio interface or with MIDI controllers (Focusrite and Novation respectively). I use Ableton Live Lite because, thanks to drum racks, I don’t need more than 8 channels for what I do. Obviously that doesn’t work for everyone. Also I got loads of really impressive plugins - from the likes of Softube and Puremagnetik, for example - free with those hardware devices. In addition, many amazing things are out there for free, from Micah’s Puremagnetik Ableton packs and plugins to Tom Erbe’s selection of free VSTs.
iOS:
Finally, there’s not really any such thing as an outdated iOS device where music is concerned. Even an ancient iPhone can be connected to a cheap iRig device and turned into an array of effects boxes, for example. Plus, it’s an obvious thing to say, but buy an iOS app once and you’ve got as many units as you have iOS devices.