I'm currently in the middle of a Saka campaign and I agree that the hardest thing about playing them is the lack of a good economy. What I did to overcome this problem was build pastoralism whenever possible. By carefully budgeting your money and saving up for caravans, markets, farms, roads and Druvaspa religious buildings you can slowly build a decent income. The only problem with pastoralism is you will not be able to recruit your basic HA's, but you will be able to build walls and recruit foot archers and saka spearmen, which make it easier to defend your settlements.