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I had just finished my tyranid army right when the new codex came out which made my list not enough points and me very mad. Can anyone advise me the cheapest way to finish a new army because i really don't want to buy to many more models in my current financial state. The army is only going to be used in friendly games and so far i have - 50 termagaunts, 3 zoanthropes, 1 tyrant without arms attached yet, 2 carnifexes, 1 yet to be built carnifex, a broodlord, 14 genestealers, 20 hormogaunts, and 6 warriors with arms still to be attached.
The best way to make a swarm cost more points is to buy lots of expensive biomorphs, implant attack, acid blood etc. Dish out regeneration on your four big bugs and it will eat up a fair amount of points. A thorax swarm for the Hive Tyrant or armoured shell will beef up it's points value quite a bit. Obviously more expensive weapons will be helpful too.
You may not want to buy more stuff but perhaps you can convert. Turn one of those Tyranid Warriors into a Tyranid Prime. Just add more spare parts to it, carapace etc. It can be given a bonesword and lashwhip which will have to be made some way, but there are quite a few ideas out there about how to do that from spare bits. The Prime will cost much more points than it would of it it remained a common Warrior. Give it adrenal glands, toxin sacs and regeneration too.
Give that Broodlord whatever upgrades you can. Things like an implant attack will make it nastier and more expensive. You could also convert one of the Zoanthropes into the Doom of Malantai, it costs more than the average Zoanthrope and it's super-nasty.
Thank you for the advice. Will the list be playable though or will i get destroyed by most enemies?
Generally speaking, simply beefing up units for the sake of beefing them up is not a good idea if you want to be competitive or have a high chance of winning games. However, just like Leech says, it's probably the best way to easily make your army bigger.
If you still want to buy some new units to complement your army though, I would suggest a trygon, which can land at around 270-ish points if you upgrade it, it's an awesome model and quite effective to. It also sounds like you could use some extra anti-tank action, and if you feel you do, i would suggest either a unit of hive guard, or to convert one of your carnifexes into a tyrannofex with a rupture cannon, both of them, but especially the tyrannofex is rather expensive pointswise.
You could naturally both upgrade your units and get a couple of new ones if you want to do that, it could be the best option for you.
"I have seen you humans, trying to forge an Empire in the name of a corpse"
I second the trygon and/or hive guard additions. You have a solid base list as-is. You could add a trygon for about 50.00 usd or 3 hive guard for 60.00 usd. Less if you ebay it or find a good deal elsewhere.