Changing the fuel pump is definitely something that you could do yourself. There are some great videos out there that can help walk you through the process. It is also really helpful to have the repair manual for your specific vehicle; especially if you will be doing other repairs yourself in the future. This is a good resource for repair manuals http://community.cengage.com/.../...g-on-a-car-repair

According to Alldata, replacing the fuel pump on a 1990 Lexus ES250 requires fuel tank removal... This is not that easy

The fuel pump is located inside the fuel tank and accessed from the top of the tank. Located under the rear seat. Pull the rear seat bottom out, and there is a circular access panel access with two plugs. Unplug and then remove the mounting bolts, lift out, and replace the pump.

Try these on-line resources for the replacement parts: www.autopartswarehouse.com, www.partsgeek.com, www.rockauto.com, www.partstrain.com - to list a few.

For example, they (RockAuto) list the replacement fuel pump and strainer from around $77.00 for your vehicle.

Fuel pump assembly = CARTER part #P72227 Pump & Strainer Set - or it's equivalent