Go a 9# mate, ideal for everything from Barra, Tuna, Queenies , Trevally but also not too heavy for smaller species , Buy what you can afford, you can always upgrade later 

+1 on the 9 weight - will be more versatile than an 8 in windy conditons too

Have a look at the Templefork Outfitters BVK series (Lefty Kreh designed) for a good rod at a great price.

At the Yellowstone 8 weight rod shootout it came in third overall and well above some higher priced rods - great value rod for the money

http://www.yellowstoneangler.com/gear-review/2014-8-weight-shootout-g-loomis-nrx-orvis-h2-sage-method-sage-one-tfo-bvk-scott-s4s-beulah-opal-best-saltwater-fly-rod-fly-rod-comparison

 After doing it once with a 9, I wouldnt be chasing tuna again with anything less than a 10.  Particularly longtails.  The 8 weight BVK is a totally different rod compared to a 9wt.  The 8 will be fine bonefishing and light salt work but the 9 has got alot more power in terms of bombing out long casts and pulling on fish.  I have the 8 and I think you probably cant beat it for the money, but again its no rod to chase pelagics with.  The 9 or 10 would be a better choice but I would favour the 9 or 10 TiCrX purely for pelagics.  Lots more lifting power.  The BVK will be nicer to cast all day with.  A shooting head style line like the rio outbound and one false cast and they will cannon out a fly a long way.

+1

#10 plus would be the go on tuna - going to need a bit of lifting power in the rod