We do almost 100% of the robot in house. Assuming you already have a cordless drill and a drill press; here's how I'd rank our advanced tools...
1. Metal Chop Saw is probably our most used tool.
http://www.amazon.com/Porter-Cable-1.../dp/B0000222X3
2. Disc / Belt Sander is a must as well, and get extra sanding discs and belts.
http://www.amazon.com/708598K-JSG-6C.../dp/B00005NMRO
3. Tig Welder would be next, as others have said, 150 Amps minimum
http://www.denlorstools.com/home/dt1...hob500425.html
Accessories would be 2 Argon tanks (one always runs out on the most important day!), 2-3 helmets, gloves, electrodes, extra ceramic torch ends, filler and a nice flat metal table.
4. Vertical Band Saw, 14" is good. Get extra blades. Local hardware stores usually only carry blades for cutting wood. So be sure to get blades that are 1/4" or so wide and have 12-18 Teeth per inch.
http://www.rockler.com/product.cfm?page=21646
4. Manual Mill... The 3-1's are iffy and would not recommend them. As others have stated, half the money goes to the machine, the other half to the tooling. DRO is so helpful. Our has a DRO retrofit which works just fine.
5. CNC Benchtop Mill... We use a CNC Jr. from CNC masters, and there are others as well for ~$10-$20,000. Don't retrofit your one and only manual mill. Once you have a manual mill and all the tooling, you don't have to go get more tooling for the CNC mill. BUT you should figure in the cost of software. We use MasterCAM which is AMAZING.
6. Arbor Press and a set of broaches (keyway and hex).
http://www.dumont.com/prod2c.html
http://www.google.com/products/catal...wAA#ps-sellers
7. Lathe... We have a small benchtop lathe to turn down shafts and such. Unfortunately it doesn't allow us to deal with things larger than an inch. We rarely use the lathe.