It's really not that expensive to get into DIY if you shop around.
Using Scubabatdan's Ejuice calculator which includes a Cost Calculator, and plugging in costs from suppliers I always order my stuff from it costs me roughly $0.083 per ml. Of course it's a tad more if I factor in shipping costs, but even then compared to the average $0.60+ per ml from most vendors, DIY is a very cheap alternative.
If you already have an idea of what flavors you enjoy, you can get them for dirt cheap over at ecigexpress, the cost of mixing equipment is negligible, safety equipment isn't all that expensive either and not really necessary if you're mixing 36mg base.
I knew I loved Virginia flavoring, it was my all day vape for about a month until I got sick of paying $20 for 30ml of it - tried my hand at DIY, failed miserably the first few times but I always mixed small 3ml batches to test so it wasn't expensive mistakes, and now I've got my Virginia 24mg 50-50 VG/PG down to a science
Finally to answer your question

a lot of people have reported getting it from pharmacies, farming supplies stores, and then there are places like this one:
VoyageurSoapAndCandle: 250ml of VG USP 99.5% for $3.10