LB you cant go wrong with Alex Sandro and at RB Danilo, Both brazilian and both very young at the start of the game, I'm in my 4th season and both have been getting interest from Barca, Real and Man City for the past season and a half, Had offers of over 25 million for both but turned them down flat.
Not sure where they will be now as 5 seasons in they will most likely have been snapped up but worth looking up for sure as they could be getting used as backup so still cheap enough and both will still be young so plenty of years left in them both.
Looking for players who will be coming good though is'nt really a good option as the prices are going to be alot higher, With 30 million you're going to struggle to find a solid LB/RB and CM if you want players who are already good, Possible but only really a good idea if you have the depth and quality in your team already to cope with only 2-3 new signings.
You can pick up some solid players for free after a few seasons, Picked up Delph for free at the start of my 4th season, Not a world beater but a solid CM until my regens come of age, Older players too like Lampard are up for free, Wages are 40-50k but you get alot of experience in the team and great tutors for those regens you buy.
Dont overlook loans neither, I've been using my maximum loans allowed since i hit the EPL because i want to save my transfer money for where i need it the most, Man City are a great team for getting loans from, Season after season they bring in new faces and just dont seem to beable to sell off the dead wood, At 250-500k fee plus 50% or so of the wages you can get a few quality players for a season without breaking the bank rather than the 10 million or so it would cost you for them not to mention the full whack of the wages.
I had Richards, De Jong and Santa Cruz for 2 seasons that cost me 1.6 million in fees both times around, Around 30-40k wages a player too ofcourse but to sign them it would have been 30 million, Same players only 10x cheaper and half the wages.