It can be as easy or as difficult (cheap or expensive) as you want it to be.
If you have a measuring cup in the house, a childs medicine dropper, a couple different sized mason jars,
a few empty juice bottles, all that's left to blow cash on is the flavours, the nic base and 500ml of pg and/or vg.
The flavourings can be hit and miss. Get 10ml sizes to start, make small 5ml trial batches.
Trial single flavours to get the proportions to your liking. Once you get, say for example, the strawberry proportions right and say you have the banana proportions right, begin mixing the 2 together keeping track
of the proportions of the 2.
Grab a few of the fruits you like, a vanilla custard(or vanilla something) as it may sweeten and take the edge off the fruits if needed. Get a weak, 48mg/ml nic. base in the beginning, this way no one will get hurt too badly if there is a mix-up somewhere. Nic in the trial batches is not needed imo. it just complicates things.
Don't toss any of your "failed" trials, once you have the trial tweaked to your liking and make a larger 30/60/100ml batch, the "failed" trial should mix in nicely without incident.
Of course I didn't do all these things when I started, take what you want, leave the rest.
Advice is cheap, free advice can be costly. DIY does NOT have to be expensive.
Any recipe you find online may not be to your liking, you may get lucky however and find some recipes that work well for you. (Cutting out a lot of trial and error).
HAVE FUN with it, make it your own, Cheers.