If you're only going to do one gun, its probably just more cost-effective to let someone else do it.
If you have more than one gun, and like better sights than what Glock ships them with, then its well worth the money to get a proper tool. Depending on what type of sights you like, you can still usually find pretty good deals/sale//discounts, etc, on the web, if you bother looking.
Ive used a couple of the MGW tools, and they work great. Their SIG tool does both the front and rear sights and has witness marks to get you mechanical zero. The Glock tool only does the rear, and doesn't have the witness mark, but I always end up with them off to the right anyway. Another nice thing about the MGW tool is, you dont have to take the slide of the gun at the range to make adjustments. Just lock the slide back and slip the tool on.
I also have one of the NcStar "universal" type tools that will do a lot of different guns, but as with most things "universal" its not perfect. And its a bit of a PITA to use. But it "works".
I paid for both my SIG and Glock MGW tools by selling the old night sights I removed from used guns I bought and/or guns I had on eBay. Dont know why people are willing to pay so much, but I usually get about $35-40 a set there, which always amazed me. The average cost for a new set of Meprolight three dot night sights that I was usually replacing them with, was costing me about $55-70.
Glocks are really very easy to do if you have the tools (front sight tool, Loctite, rear sight tool, and a piece of fine emery paper). Its about a 5-10 minute job once you've done a couple.
The front sights are pretty much self explanatory, just make sure you use some Loctite, or they will come loose.
The rear sight, just "push" the old sight off, left to right (looking at it from the rear), and "pull" the new one on from the right to left (it matters). Before you even start, run the bottom of the new sight across the sheet of emery on a flat, hard surface, until the black finish on the flat bottom is pretty much worn off. Dont get too crazy, but this is how you adjust or fit the rear sight to the dovetail. Usually, just removing the finish is all you need to do, but sometimes, you may need to do it some more, if its really tight and doesnt want to move. One small drop of oil wiped across the bottom of the dovetail usually helps too.
If youre cheap, and dont want to spend the $$ for the tool you can use a punch and hammer on the rear sight, if you like to struggle, but I would not use that method if youre installing night sights. Never made any sense to me to be beating on them and maybe breaking or compromising the vials. Its also a lot more of a PITA to try and get the zero right.