if you buy several cheaper...errr...less expensive cogs you can experiment with different ratios for a smaller investment

redline, gusset & avenir make machined steel cogs in 3/32" that you can easily find online for less than $10

i have ridden a gusset 332 cog for thousands of trouble free miles...but once you find the size you like best you can switch to something like a soma or eai that will get you more cred here, if that is what you crave...