You should be able to find a handful of hosts that meet your requirements under your budget (your budget is larger than many other seekers around here!). As HF mentioned, you can take a look in the offers forum, or you can simply browse the reseller forum and see what hosts have been talked about and reviewed, etc.. and generate a list of possible hosts!
You may want to look at some directories of web hosts such as the ones mentioned above, also try www.webhostdir.com
Also i recommend checking out the hosts technical support to, maybe send in a ticket to see how long they take to respond, or maybe visit their live chat if they have one or not. As you will need good support to support your clients.
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With $40-50 I would go for a VPS (if you know the basics of server management). It will give you a lot more privacy and generally VPS/dedi companies are nicer to deal with. Futurehosting.biz have good VPS's and for about that price will get you everything you need. 10GB and 100GB on a shared plan for me means a lot of overselling.