Such a massive waste of money. These solutions are worth maybe $100/each if they were optimal sizes which they are probably not. I got a 512gb server a couple month ago (black friday deal) for $350/month. Then you buy a multi-way pre-flop solver for $300-500 and run as many solutions as you want.

I´m a student and can´t afford 350€/month.
So what are my choices to work on my preflop game?
Basically only to buy solutions, right?

Buying a solver and a server is not an option for me.

How is it 2019 and preflop 6max cash is still a mystery.
I could afford these solutions, since I only have to buy them once, while I have to constantly pay for a server.

I´d much rather get preflop solutions and then invest into GTO+ to work on postflop, but there is no point in working on my postflop fundamentals when my preflop game is based on intuition.

Use snowie free preflop advisor to build a base. Solver solutions are slightly different but its a decent tool for no cost

If budget is a constraint then the only option is to use what the preflop advisor gives and intuition. So in your example you can take btn 3b range versus ep/mp rfi and adjust it to account for co cc, typically tighten range up and focus on suited hands as you’ll need to get 3b through more players and have a higher likelihood of going multi way. I’d guess you just play a linear 3b range and probably fold or flat more of the low suited connectors that snowie might mix against only an rfi range since you block the folding ranges. So yeah, just try to use intuition and make the best adjustments you can and figure it out that way until you can afford to get solver ranges or find someone that will share them.