I agreed that monster bike is nice, but few things you might want to reach for a bike around your budget. 1, Over All Quality which I would say go for some big brands such as Pitsterpro, Motovert, or I heard someone sale the brand called Azreal that is a very reputable race team brand from Spain. 2, Race Durability: that means how long your bike can stand out in the ring without some junk bikes come out from no where and smoke yours just cuz the motor is bigger. Therefore again only big brands would offer something unique such as Pitsterpro GPX USA 150cc 11.8HP, Motovert Daydona SOHC 11.5, Azreal 150cc 13HP or you can always get the SGR big bored kit 146cc around 12 HP. 3, Appearance: within that kinda budget of yours, you should deserve some WOW while you flash out your bike in the ring, which some standardize the blings are necessary but make sure they are CNCed. Also some little thing you might also want to take a close consideration. Some parts on those big brands they are again unique not to mention they are perfectly fit into the colour combination, which will eventually deliver a splendid appearance of the bike. Last but not least: You will always buy the bike from a reputable store, cuz you always will be looked after if anything happened to your bike. For sure buy bike from store they might bit more but how about some little corner stores and those ebayers? I don’t think they can turn up at your door step say "no worries mate" I got ya coverd.
Good luck for find yourself an amazing rider mate, pub some nice pics when you got one.