I would guess at $4000 to $5000 with a lot of "IF's". Tires older than 5 years by date codes on tires should be replaced with correct types and quality brand. Tires develop sidewall cracks sitting parked and can come apart underway, causing loss of control and tearing up holding tanks,propane lines and wiring. The brake system must be in good shape including flushing of brake fluid and replacement of flex lines to front brakes. Water damage is hard to repair and expensive. Such things as roof AC units, dash AC units, engine cooling system, house batteries and converter charger, fresh water pump, fridge, water heater, RV generator, awning fabric are all expensive to replace. Get estimates in writing for any repairs needed to decide whether any used/old rig is worth buying and can be made safe to drive, within your budget. You can easily spend $10K on repairs and replacements to make an old RV safe to drive and fully functional. If you really have a lot of skills, tools, workspace and time, you can save some 50% in repairs and replacement costs.
