With a Database that size and with that much traffic, I can see how it could shut down a server with more than likely 600 accounts on it. A VPS would more than likely get you out of anymore issues with these cheap hosts, but like you said, you have little budget for this.
You can get a half decent VPS for around $20 - $30, maybe cheaper, but remember you get what you pay for
Have you ever thought about selling advertising from your site ?
With that many visitors you shouldn't have any problems finding companies that will bite your hand off to get a banner on your site.. just a thought
a good vps will handle that (layer0) no need for a full dedicated, but others may not agree.
A good VPS that size is close to the price of a dedicated anyway. He's in dedicated server realm, but totally unprepared for it. This is the very danger that highly oversold shared hosting presents to the market: unreasonable expectations from unaware customers.
WN-Ali's advice is sound. Your primary focus should be to make the site pay itself. Google Adsense can be a fast, easy way to get the necesarry revenue, but not necessarily the optimum one. If Google Adsense doesn't bring in enough, there's still the option of selling advertising space directly to third parties who can effectively market products to the particular audience your website has.
Amazing really that the site is still running given the load it must be putting on the server. Seems that the Bluehost policy of short time-outs allows the site to stay (albeit with downtime) and the server to keep working.
I very much agree that the focus has to be on making the site pay enough to get a hosting that can take that amount of pressure on the CPU. Alternatively, to find a way of reducing its popularity so that it can be afforded.
Do they both provide managed servers at those prices? How much sysadmin is included (& what is the price)?
What about cpanel etc?
How much of this are you confident in being able to do yourself?
The difference between a shared account with cpanel & lots of one click installs and management tools and a dedicated server is pretty big.