You can get them from tons of places for tons of prices, I'll run through a few of the more common ones
Mr limpy/ mr packy/ packy/ etc: basically any adult store or trans website, cheapest packer, generally $10-15 (maybe even less) depending on where bought and what size . Comes in four I think, the most common are 3.5 inches and 5.5 inches
Masho: tranzwear, queen cat, amazon, I believe $12-17 but possibly cheaper. This one has 3d balls and is 4 inches
Sailor soft pack/ GV soft pack: good vibes and some other stores like it I think, most trans stores, amazon, $20-25 (maybe as high as 30), 4.5 or 5.5 inches, firm inner core supposedly more realistic
Reel magic basic packer: reelmagik, $80 if I remember correctly, but about $100 or more with shipping, this is basically an inexpensive packer made from a prosthetic mold. It's probably the most realistic packer without going into prosthetic category. 4.5 inches.
As for comfort of different packers, that is totally a personal thing. I've never found it uncomfortable but it can be awkward at first. You may want to look into harnesses for whichever you chose if you'll be wearing it in P.E.