The regional park is great, and because of where I live, I normally enter through the southern entrance. Keep n mind that there are lots of other trails in the area as well. If you haven’t seen FINS yet you are in for a treat. There are also a lot of other trails in the area of you look hard enough.
I bought a $400 bike from bikesdiret and love it. I’ve upgraded it since then quite a bit, but most people don’t need to spend $5000 on a bike. You can ride just fine for a decent price. Don’t be a price snob. Do what works for you.