I’ve done the same but not with juniper products. And always get the best your budget will stretch too.
If you dont have the budget to buy new then the only option is second hand. If you know juniper products then you know what you want its more a case of what can you afford and where can you get them.
I went secondhand Cisco which did the job BIGTIME and after much heartache I found EBay the answer.
I found the 800 series router to be fine, i then went for Cisco 1900 and 2100 switches. Pix firewall (EBay)
Cant really help on the juniper products as not worked with them but for routing and switching Cisco are hard to beat and If you can work the IOS you can work and understand most other products.