You'll look better dressed than average if you just get clothes that fit (FWIW, my experience is working for the government in an engineering field - not the best dressers overall).
First, if you want good inexpensive shoes, see the CT sale thread from last night/this morning. I am in the same boat as you, just starting my job out of school. I'd start with a couple of pairs of more conservative shoes that will be versatille, say the black semi-brogue and chestnut derbys. Later you can move on to the chukka boots and wholecuts when you can afford other brands with last shapes more suited for these styles (EG, C&J, Lobb).
As for pants, you will have to get them tailored for them to look good, so make sure to buy up an inch if things feel snug in the waist, and/or short in the inseam so there's enough material for alterations. I'm pretty sure there is a SYMS nearby that would carry a good selection of pants. You can get some HSM wool pants for $80 a piece and pay ~$10 for hemming and look great. I've always felt that most dress trousers are pretty bland anyway, but that's just my opinion.
Shirts, ties and shoes really make the outfit if you aren't wearing a jacket. Here is where I'd spend my money. Having a large variety of shirt and tie combinations where most everything matches everything else can make only owning just a few different pairs of pants serviceable in a starting wardrobe.