Simple firewall with VLAN and stateful packet inspection

I was hoping this was an easy question.  I have experience with RV042s at one end of the spectrum and Juniper SRX series at the other.
 I don't think the RV042 will meet the requirement and I am looking for a standalone *of that sort* that won't require the SRX.  

You need at minimum a security appliance that offers DPI

No, I meant what I said.  I need at a minimum a security appliance that offers SPI.  This, to meet a specification.  I would contrast this with NO SPI which I'm sure is easy to obtain.

I can't really recommend a particular device because I don't know how many users you have or how many connections are running.

I said the data rate was low.  How will a count of connections or users help modify that?  If you must: One connection and one user and very transient at that.
Thanks for the reply.  I'm hoping that something at the "low end" will do the job.

Thank you both!
Blue Street Tech:  Sorry, I somehow missed your recommendation at first.  I guess I got focused on "can't recommend".  :-(  That's exactly what I was looking for!
masnrock:  Thanks for the alternate suggestion!

No problem. Glad I could help!