If you are doing terrain, then get down to the local DIY store, and get a tester pot of brown/earth colour emulsion done up ASAP. You don't need hobby quality acrylic paint for 90% of terrain painting especially the base colours.
Not sure where you are based but in the UK, a small tester pot (250ml) is yours for £5.00 GBP-6, whereas an acrylic pot (20ml) is £2.00 GBP-3 – NO CONTEST !
Once you have identified the colour of preference, you can have pots of emulsion done up for £15.00 GBP for 2.5litres which goes a long long long way.
I have 5 pots of emulsion on the go covering all my base colour needs for figures and terrain. And I have had enough to hand on to mates in small pots for free. As one of my mates has also turned his hand to producing terrain for some of the tables of scenery we field it means his stuff fits in 100% with the rest of my stuff.
If you do go down this route, consider keeping the plastic tubs you get food sauces in (curry/pasta) and invest in a soup ladle so you can keep small pots of the emulsion on the go preventing the bigger can drying out…and also your wife/partner getting annoyed at your use of serving spoons). ;-)
If your base material is fragile, you might also consider covering the material including the sides with PVA (white glue) before painting as well. Again, get down to the DIY shop and you can pick up pots of the stuff at prices far cheaper than model/hobby/art shops sell it for. I've got through two 1litre tubs of PVA in the last year so fast it didn't have time to form a skin.
Similarly, I have invested in "Ready to use Plaster repair and skim" tubs of filler (1 litre) for scenery and figure basing purposes. You can get various types including ones that flex if you think you need it (wood filler is good). Again way cheaper than model specific putty and will cover a feck load of scenery easily. You can get large hobby spatulas to spread it or even "grown up" building tools.
You might also try out your local motor repair store (Halfords in the UK, aka Hellfrauds), for cheap black primer and I've even found textured sprays in there was well.
Sorry on a roll, as I have just done a round trip through town today loading up on all of the above having blitzed a load of scenery in the last month.
HTH
Giles.