This is not true, when you do something halal you get rewarded for it, either you get money from it or not.
For example, if you die while working or going to work because you have a family and you want to assure them food and world benefits, then you will be conidered as a shahid (killed for the sake of Allah). Working is jihad.
If you refuse a job that contains haram, like working in a bank. Then you get rewarded for your choice, and everyday you have difficulties because of this job is rewarding for your patience.
If you do something for free or for a cheap amount, then the money you could have earned from your activity will be considered as Sadaka. But also if you sell goods to help muslims live a better life, choosing that goods in the intention to bring benefits to muslims will be rewarded, even if you make money from it.
Don't forget everything is free at the basis: vegetables and food grow for free, the land is given to us by God for free. What you pay is only the time people spent to make things: a farmer spends time with his sheeps, and that's why you pay for meat (even if the sheep was eating free stuff from the ground). When you buy a car, you pay people who took the free metal fromt the ground , that metal that God made available for us for free. you pay the engeneers for the time they spent to design the car, you pay for the people who designed the machines that make the car. but at the end you only pay poeple for their time.
So using your time for halal activities is a source of rewarding, even if you get payed for it, since you listened to God's orders and didn't follow the haram path