Welcome to the party!
You can play with any amount of points, it'll depend on your opponent. Common numbers are 500 points, 700, 1000, 1500 and 2000 point matches, but it's up to you and the person you're playing with to decide.
If you're looking for prices for basic 1k point forces (this is just a basic force, not accounting for how good it'll be vs others who spend more on other units etc.) here are a couple of ideas:
Chaos - half the start set (go halves with someone, or sell half the models you won't need on ebay) and a start collecting set for £88 will get you:
1 Blood Secrator 120
1 Blood Stoker 80
1 Khorgath 80
5 Blood Warriors 100
20 Blood Reavers 120
1 Slaughter Priest 100
10 Blood Warriors 200
3 Mighty Skullcrushers 160
Total: 960 points
There is also a list for Stormcast which will cost you the same, again just get the starter set and a SC box and sell the other half:
1 Relicator 80
1 Lord Celestant on Dracoth 220
10 Liberators 200
3 (5) Paladin Retibutors 220
3 Prosecutor With Celestial Hammers 100
3 Prosecutor With Stormcall Javelins 80
5 Liberators 100
2* Paladin Retibutors (Additional) ***
Total: 1000
For Seraphon specifically buy a Start Collecting box, convert a Starpriest, buy a box of warriors and a box of skinks and you get this:
1 Skink Starpriest 100
1 Old Blood on Carnosaur 320
5 Saurus Knights 120
10 Saurus Warriors 100
20 Saurus Warriors 200
20 Skinks 160
Total: 1000
Costing you £94...
There are tons of options. What do you want to do with your army? Who will you be playing against? What kind of matches? Do you have a local meta to compete against?[/QUO
First of all ty for the positive feedback idk yet on the local shop what they playing i think they play a competitive i am not sure to be honest yet.But when i asked they told be i shoukd bring at least 1k do ill be able to play

so i wanted to start with either seraphon either skaven or u dead legion.