Ebay is a great place to buy second hand miniatures.

Miniatures by post is a good place to buy new warhammer it has a 20% discount on most games workshop products.

Unit fillers can help to stretch the models you have further, for example you could have a 50x50 base in a orc boy unit with two orcs fightin da wrong team.

battle for skull pass is a good way to get started but also could be good for expanding an existing army it has 540 points of goblins in there not including magic items and you could sell the dwarves.

Boar boyz are expensive so dont buy the metal ones save up the riding legs you get in the orc warriors sets until you have five or ten then buy the boars and put normal orcs on the boars.

Black orcs and savage orcs can be made out of the orc warrior set.

more goblins can be made out of the goblin regiment set.

a spear chukka can be scratch built.

the Snotlings that you buy could be split into three bases instead of two, all you need is an other swarm base.

how to start an 1000 point orc and goblin army for £36.
first buy two orc warrior sets assemble them as one of them as big uns (use lots of shoulder pads)
and the other unit as savage orcs.
use this list. you will find there are 38 models that you bought and 43 models this list uses. to get round this
use unit fillers.

savage orc shamen 155pts
level 2
dispell scroll
power stone

orc shamen 150pts
level 2
dispell scroll
power stone

black orc b boss 164pts
battle standard bearer
heavy armour
warboss umm's best boss 'at
nibbla's itty ring

20 orc boy big uns 300pts
spear's
shield's
morks spirit totem

20 savage orc boyz 230pts
extra choppa's

total=999pts