I don't know the gsm conversion to the pound designation. If you have a store nearby like office depot that has lots of demo units on display you can take several pieces of card stock. Start with the smallest and work up to the one that works. You will need a straigt paper path for heavier stock so you need a printer with a door that opens in the back for paper to exit instead of making the "u-turn" to come out the top and an auxilliary feed in the front. In addition, if you are planning to print multiple copies at once you will need both the aux front paper tray and a rear tray that will stack printed cards for multiple copy runs.
Sorry to tell you this, but I found that the least expensive printers didn't handle card stock well, the fusers didn't get hot enough to set the toner, and the gap at the fuser wasn't wide enough to accomodate card stock without risking damage to the fuser assembly. Starting with the least expensive printers I fed them envelopes and the card stock I sometimes use until I found the one that didn't munch the envelopes or leave the toner in a state that easily rubbed off. I ended up with HP P3005 - not an inexpensive printer to purchase or buy toner carts for, and certainly not small by any means..
With laser printers, on some you can set the fuser temp by selecting a thicker paper and its ajusts accordingly to compensate for the extra heat rerquired. Also I heard there is a new OKI laser outy that takes 400gsm.