Otherwise, if you wanted build one, check out any of the RCA tube manuals, as they all have a preamp circuit pretty much after the 1951 editions. Most built around 12AX7's or 12AU7's (european equivalents in ECC82 and ECC83). There are also many to be found online.
You will tend to find more differences in the tubes themselves in some cases, moreso than the brand of preamp. Some brands may offer more bells and wistles than others. But all ready made preamps are going to be spendy.
:Wondering what is a really good make and model single ended tube preamp? I want to run a mike into it and then into my computer. Thanx