I've taken Luton to the Premir League. with back to back promotions apart from season 3. BSP>L2>L1>L1>CH>Premier League. I got relegated in my 6th season and took over at Leicester. BTW the boards expectations are high. Every season I was at least expected to win promiton until Season 2 in League 1. When I was told I had to finish in top half. Champ (top Half) and Prem (Avoid Relegation)
Basically, all the way up you have to rely on free transfers and loans coz you aint getting any money.
First season I signed on frees James Beattie (ST). Dean Bouzanis (GK) and Jordan Bowen ML. There are few more, out there but I think they're the only 3 i signed first season. Then bought in Paul Downing (CB) on loan. and bought in Ryan Noble on loan in January/February time.
Also, To save wage budget, release all you reserves you should have enough in the first squad for the seaosn (I did)
Have a scout, scout the reserves and one scout the League above every season. That way at the end of the season when good young players get released you'll know by the recommendations. Conor Newton is a good one from Newcastle. Try and extend Downing's loan all the way through your run.
There is one major problem, contract renewals. You have no money to improve offers, so at the end of the season you release a few players. Try to keep Keith Keane as long as possible. Also, if you have players not playing (not through injury but just not needed) release them, because come the next season it's valuable wage budget.