Check out www.spamexperts.com - for SMBs/ Enterprises, at 250 users, you'd be looking at $4.74/ user/ YEAR for our hosted solution (minus 10% for Spiceheads, so effectively around $4.25/ user/ YEAR). If you can put me in touch with your webhost, I'm also happy to reach out to them as we offer very attractive reseller pricing so perhaps that will allow them to offer it to you even cheaper. Free trials are, by the way, available at: http:/
[EDIT: marketing just scolded me... it's 20% discount for Spiceheads. So roughly $3.75/ user/ YEAR]