Eh. My greatest success story was with one of the lower league teams in Portugal. Picked randomly. Actually, it was a 3rd tier team. But basically, it was a semi-professional team, dismissing and signing an entire squad every season. Free players only. 0 budget. 6k wages per MONTH. That's like what, 1,5k per week.
I found better players than the ones I had on free transfers. As I performed better, specially my forwards, I could sell them for a price. First a miserable 50k, then as I performed better and played on higher leagues, I could sell them for a higher price. 250k, 500k, so on. All while getting better players on free, or for low amounts like 50k, 90k. I was able to invest on players for 1M after 5 seasons, and I was champion of the 1st division after placing 6th 2 seasons in a row. All of this took 6 seasons or 7, to be champion. I sold on player for 33M to Blackpool that I bought for 90k when he was 16 (he only joined the club when he turned 18 though). One of those rare regens that was incredible. And as I made money, I bought better and better players. I never spent more than 5M on one. I had losses every year, and sold players to make up for it. And one seasons... I won the CL. Just like that. Against everything. I had never gone beyond the last 16. I don't know. It just happened. All of the ties in extra time, or penalties, while being one man down, etc. Destroyed Bayern 4-0 in the final. All with not top of the class players, but good players.
Beyond having a winning tactic, take your time in transfer windows. Sell your key players that will make some money for you, and in return buy one that is just as good, but is free or costs less. Your players will be your assets. You need money to compete higher and higher, so lose as many hours as you see fit to make sure you have players that can guarantee you a league position and performance that will allow you to sell them when the seasons ends. Again, sell your key players, sell your best player, I always did, every season, and go fishing for another. You can ALWAYS find something. Just search and get the absolute best you can.
I found it to be easier than I thought it would be, as my first spell with such a low division team.