You can't listen to the fanboys on these things
The losi is a great buggy, but it is costly. For someone looking at bashing mostly, I would go with something cheaper but still by a good company with a racing pedigree for hopup support. The new HPI looks good and as far as I can tell, its just the regular HB D8 made electric, unlike the HB Ve8 that has a plastic frame. Being D8 based means it should be a good racer as well will good hopups straight from the D8 side. That is of course if it is mostly D8 dna. Plus it comes RTR with what is really just a re-branded Castle MMM system, for less than the Losi chassis only. I would just upgrade the radio with a spektrum or futaba 2.4ghz radio, and a 2ch is all you will need, a 3ch will just cost you more and you won't need that third channel, most of the 2ch and 3ch have similar features. I own a spektrum dx3 and a futaba 3pm and never used the third channel. Besides those high end radios like the dx3r are overkill unless you are a pro level driver. The losi will put you near your budget after you buy a motor and esc. If your set on those choices I would say the HPI buggy, with batteries and get a Slash as well
If you are willing to branch out to other choices, I have heard good things about the new hyper 9e, there is a thread on this forum about it. Nitrohouse.com has it for $400. The new AE rc8be and rc8te look good as well. My friend is getting a rc8te soon, it looks to be better optioned than their RS spec'ed buggy/truggy but with lighter/thinner parts than the pro versions. Of course the pro version can be converted easily with AE's $100 kit, which will still be less than the losi. Caster racing seems good as well, it has a well balanced layout, and their website has a sale going on. You can get the RTR which has a pretty good ESC (the hobbywing I believe the 80amp version) but only an ok motor. The pro versions of the truggy and buggy have more options that lean to the racing side and lets you choose the electronics.
A good 2ch radio will cost about $200 with servos or $120 and 80 if bought separate. If you want to run 4cell lipo it will cost you around $250 for hardcase and $150 for softcase batts. A decent charger and balancing setup will be around $130. And if you need to get a ESC and motor that will run around $250 to 330 depending on brand. As far as the power plant The castle systems are really good especially for a basher. The tekin RX8 system is really good and smooth, but its still new and its going trough some teething issues like castle did, but tekin will fix any issues no problem, if you have any. Speed passion has a good system, and I hear its just or in process of being updated. Seeing as its really just a re-branded hobbywing in a metal casing, they are probably going to the new 150amp version. You can get a hobbywing 150amp esc for $100 or the 120amp for a bit less, combos go for around $200, but I hear the motors are only ok. If you went that route I would get the ESC only and get a quality motor for it.
For a primarily bashing car, a truggy might work better for you, so keep that option in mind.
hope that helps
Edit- just noticed you have several hundred posts, so your not a newb at RC so you probably know most of this info