Eurorack has the reputation of being expensive and a money-trap that always require to get this or that module.
The truth is that the cost will depend on you.
If you are a fanatic “dawless jammer”, then you will need a lot of modules to build a complete system that can replace synths, drumboxes, and so on.
If you have a computer, and agree to use it to control your rack in a “hybrid” approach, then it is much less costly. SOftware cost a fraction of a module, and generally achieve the work of many modules. You can concentrate on the heart of your rack, which are the analog oscillators and filters. All the rest can be managed in a PC. it allows to start right away to make sound, and nothing forbids to add more stuff from time to time, and end up witha standalone system that did not put that much pressure on your budget… because it is dilluted over time.
Thinking about your rack
This is done by building your dream rack on modulargrid, watching tons of videos demoing the modules, and checking the current prices in modular shops.
With modular grid, you will have a pretty good idea of the prices, of the power required by all your modules, and will have a good idea of the “shape” of your rack (if you want to build something impossible to find in shops).
Because it gives you a minimum price for your dreamrack, ModularGrid is great. If you want to stay within a controlled budget, you will change your approach and focuss on the aim of your rack. It also gives you an idea of the size of the different modules, and the best way to organize them inside a rack.
I wanted something where I can mix filters which are reproductions of vintage modules. For example, I absolutely wanted a 3340-ish oscillator, may be EMW 104 oscillator because it reminds me of early Yazoo style. For the filters, I want to be able to have 2 filters, such as a classic 24dB lowpass, a jupiter-ish filter, and and enough empty space for “something else” just in case (filter or else).
As I will build it slowly, I am pretty sure that some modules that I will finally get are not even released yet, so I needed the ability to extend the rack easily if I ever need it.
My rack had to be minimum 2 rows of 3U, with the possibility to extend it by 1U or by another row of 3U.
Units (from what I learned on the net)
3U is the height of eurorack modules. it is 13 centimeters (or very close to 13 cm)
MU is the size of vintage Moog modular. It is nowadays referenced as MU or 5U.
HP is the unit of width of each modules in Eurorack format. 1 HP is approximately 0.5 centimeter. Modules can be as narrow as 2 HP, and as wide as 80 HP or more (synths that can be put in eurorack cases). Oscillators and filters are often between 4HP and 16 HP width.