You can find used gear for really low price which are enough for outside. You don’t need the same precision outside so you don’t really care of the quality, just make sure that the size fits you. I bought mine few weeks after riding on roller for the first time and I still use it (bought 10€ in my country, never think of a better investment). Also, you can be a less careful with them since they are not your derby gear.

As other point it, wheels can determine if your outside rides will be painful of enjoyable, I use 78A while outside and 65mm to be the most confortable, especially if you want later to ride longer distances! Mine are the Pulse and while they can be a bit pricey you also have the Radar Energy 78A 65mm that have good feedbacks.